add a contributing guide

Questions about how to contribute come up from time to time, eg:
https://github.com/scottlamb/moonfire-nvr/issues/84#issuecomment-656065208
https://github.com/scottlamb/moonfire-nvr/issues/68#issuecomment-688938108

I hope this helps answer them. I think github adds a couple links to
a file called CONTRIBUTING or CONTRIBUTING.md so this filename gives it
some extra visibility.

.github/ISSUE_TEMPLATE/bug_report.md

@@ -22,7 +22,7 @@ A clear and concise description of what you expected to happen.
 
 **Server (please complete the following information):**
   - If using Docker: `docker ps` + `docker images`
-  - If building from git: `git describe` + `moonfire-nvr --version`
+  - If building from git: `git describe --dirty` + `moonfire-nvr --version`
   - Attach a [log file](https://github.com/scottlamb/moonfire-nvr/blob/master/guide/troubleshooting.md#viewing-moonfire-nvrs-logs). Run with the `RUST_BACKTRACE=1` environment variable set if possible.
 
 **Screenshots**

CONTRIBUTING.md

@@ -0,0 +1,114 @@
+# Contributing to Moonfire NVR <!-- omit in toc -->
+
+Hi, I'm Scott, Moonfire NVR's author. I'd love your help in making it great.
+There are lots of ways you can contribute.
+
+* [Saying hi](#saying-hi)
+* [Asking for support](#asking-for-support)
+* [Offering support](#offering-support)
+* [Filing bug and enhancement issues](#filing-bug-and-enhancement-issues)
+* [Contributing documentation](#contributing-documentation)
+* [Contributing code and UI changes](#contributing-code-and-ui-changes)
+
+## Saying hi
+
+Please say hi on the [mailing
+list](https://groups.google.com/g/moonfire-nvr-users) or in [github
+discussions](https://github.com/scottlamb/moonfire-nvr/discussions) after
+trying out Moonfire NVR. Often open source authors only hear from users when
+something goes wrong. I love to hear when it works well, too. It's motivating
+to know Moonfire NVR is helping people. And knowing how people want to use
+Moonfire NVR will guide development.
+
+Great example: [this Show & Tell from JasonKleban](https://github.com/scottlamb/moonfire-nvr/discussions/118).
+
+## Asking for support
+
+When you're stuck, look at the [troubleshooting
+guide](guide/troubleshooting.md). If it doesn't answer your question, please
+ask for help! Support requests are welcome on the
+[mailing list](https://groups.google.com/g/moonfire-nvr-users) or in [github
+discussions](https://github.com/scottlamb/moonfire-nvr/discussions). Often
+these discussions help create good bug reports and enhancement requests.
+
+## Offering support
+
+Answering someone else's question is a great way to help them and to test your
+own understanding. You can also turn their support request into a bug report
+or enhancement request.
+
+## Filing bug and enhancement issues
+
+First skim the [github issue
+tracker](https://github.com/scottlamb/moonfire-nvr/issues) to see if someone
+has already reported your problem. If so, no need to file a new issue. Instead:
+
+*   +1 the first comment so we know how many people are affected.
+*   subscribe so you know what's happening.
+*   add a comment if you can help understand the problem.
+
+If there's no existing issue, file a new one:
+
+*   bugs: follow the [template](https://github.com/scottlamb/moonfire-nvr/issues/new?assignees=&labels=bug&template=bug_report.md&title=).
+*   enhancement requests: there's no template. Use your best judgement.
+
+Please be understanding if your issue isn't marked as top priority. I have
+many things I want to improve and only so much time. If you think something
+is more important than I do, you might be able to convince me, but the most
+effective approach is to send a PR.
+
+## Contributing documentation
+
+Moonfire NVR has checked-in documentation (in [guide](guide/) and
+[design](design/) directories) to describe a particular version of Moonfire
+NVR. Please send a github PR for changes. I will review them for accuracy
+and clarity.
+
+There's also a [wiki](https://github.com/scottlamb/moonfire-nvr/wiki). This
+is for anything else: notes on compatibility with a particular camera, how to
+configure your Linux system and network for recording, hardware
+recommendations, etc. This area is less formal. No review is necessary; just
+make a change.
+
+## Contributing code and UI changes
+
+I love seeing code and user interface contributions.
+
+*   Small changes: just send a PR. In most cases just propose a change against
+    `master`.
+*   Large changes: let's discuss the design first. We can talk on the issue
+    tracker, via email, or over video chat.
+
+"Small" or "large" is about how you'd feel if your change isn't merged.
+Imagine you go through all the effort of making a change and sending a PR,
+then I suggest an alternate approach or point out your PR conflicts with some
+other work on a development branch. You have to start over.
+
+*   if you'd be **frustrated** or **angry**, your change is **large**. Let's
+    agree on a design first so you know you'll be successful before putting
+    in this much work. When you're ready, open a PR. We'll polish and merge
+    it quickly.
+*   if you'd be **happy** to revise, your change is **small**. Send a PR
+    right away. I'd love to see your prototype and help you turn it into
+    finished software.
+
+The [Building Moonfire NVR](guide/build.md) and [Working on UI
+development](guide/developing-ui.md) guides should help you get started.
+The [design documents](design/) will help you fit your work into the whole.
+
+Please tell me when you get stuck! Every software developer knows in theory
+there's parts of their code that aren't as clear and well-documented as they
+should be. It's a whole other thing to know an unclear spot is actually
+stopping someone from understanding and contributing. When that happens, I'm
+happy to explain, expand design docs, write more comments, and revise code
+for clarity.
+
+I promise to review PRs promptly, even if it's for an issue I wouldn't
+prioritize on my own. Together we can do more.
+
+If you're looking for something to do:
+
+*   Please skim issues with the [`1.0` or `1.0?`
+    milestone](https://github.com/scottlamb/moonfire-nvr/issues?q=is%3Aopen+is%3Aissue+milestone%3A1.0+milestone%3A1.0%3F+). Let's ship a minimum viable product!
+*   Please help with UI and video analytics. These aren't my field of expertise.
+    Maybe you can teach me.

README.md

@@ -1,5 +1,8 @@
 [![CI](https://github.com/scottlamb/moonfire-nvr/workflows/CI/badge.svg)](https://github.com/scottlamb/moonfire-nvr/actions?query=workflow%3ACI)
 
+* [Introduction](#introduction)
+* [Documentation](#documentation)
+
 # Introduction
 
 Moonfire NVR is an open-source security camera network video recorder, started
@@ -12,6 +15,9 @@ analyze, or re-encode video frames, so it requires little CPU. It handles six
 2](https://www.raspberrypi.org/products/raspberry-pi-2-model-b/), using
 less than 10% of the machine's total CPU.
 
+**Help wanted to make it great! Please see the [contributing
+guide](CONTRIBUTING.md).**
+
 So far, the web interface is basic: a filterable list of video segments,
 with support for trimming them to arbitrary time ranges. No scrub bar yet.
 There's also an experimental live view UI.
@@ -25,7 +31,7 @@ There's also an experimental live view UI.
   </tbody>
 </table>
 
-There's no support yet for motion detection, no https/SSL/TLS support (you'll
+There's no support yet for motion detection, no https/TLS support (you'll
 need a proxy server, as described [here](guide/secure.md)), and only a
 console-based (rather than web-based) configuration UI.
 
@@ -34,50 +40,36 @@ compatibility guarantees: configuration and storage formats may change from
 version to version. There is an [upgrade procedure](guide/schema.md) but it is
 not for the faint of heart.
 
-I hope to add features such as salient motion detection. It's way too early to
+I hope to add features such as video analytics. In time, we can build
-make promises, but it seems possible to build a full-featured
+a full-featured hobbyist-oriented multi-camera NVR that requires nothing but
-hobbyist-oriented multi-camera NVR that requires nothing but a cheap machine
+a cheap machine with a big hard drive. There are many exciting techniques we
-with a big hard drive. I welcome help; see [Getting help and getting
+could use to make this possible:
-involved](#help) below. There are many exciting techniques we could use to
-make this possible:
 
-* avoiding CPU-intensive H.264 encoding in favor of simply continuing to use the
+*   avoiding CPU-intensive H.264 encoding in favor of simply continuing to use
-  camera's already-encoded video streams. Cheap IP cameras these days provide
+    the camera's already-encoded video streams. Cheap IP cameras these days
-  pre-encoded H.264 streams in both "main" (full-sized) and "sub" (lower
+    provide pre-encoded H.264 streams in both "main" (full-sized) and "sub"
-  resolution, compression quality, and/or frame rate) varieties. The "sub"
+    (lower resolution, compression quality, and/or frame rate) varieties. The
-  stream is more suitable for fast computer vision work as well as
+    "sub" stream is more suitable for fast computer vision work as well as
-  remote/mobile streaming. Disk space these days is quite cheap (with 4 TB
+    remote/mobile streaming. Disk space these days is quite cheap (with 4 TB
-  drives costing about $100), so we can afford to keep many camera-months of
+    drives costing about $100), so we can afford to keep many camera-months
-  both streams on disk.
+    of both streams on disk.
-* off-loading on-NVR analytics to an inexpensive USB or M.2 neural network
+*   off-loading on-NVR analytics to an inexpensive USB or M.2 neural network
-  accelerator.
+    accelerator and hardware H.264 decoders.
-* taking advantage of on-camera analytics. This is the lowest CPU usage option,
+*   taking advantage of on-camera analytics. They're often not as accurate, but
-  although many cameras' analytics aren't as good as what can be done on the NVR,
+    they're the best way to stretch very inexpensive NVR machines.
-  they're hard to experiment with, and even when they use modern ML-based
-  approaches, their built-in models can't be retrained.
 
 # Documentation
 
+*   [Contributing](CONTRIBUTING.md)
 *   [License](LICENSE.txt) —
     [GPL-3.0-or-later](https://spdx.org/licenses/GPL-3.0-or-later.html)
     with [https://spdx.org/licenses/GPL-3.0-linking-exception.html](GPL-3.0-linking-exception)
     for OpenSSL.
-*   [Installing](guide/install.md)
+*   [Guides](guide/)
-*   [Building from source](guide/build.md)
+    *   [Installing](guide/install.md)
-*   [UI Development](guide/developing-ui.md)
+    *   [Building from source](guide/build.md)
-*   [Troubleshooting](guide/troubleshooting.md)
+    *   [UI Development](guide/developing-ui.md)
-*   [Wiki](https://github.com/scottlamb/moonfire-nvr/wiki) has notes on
+    *   [Troubleshooting](guide/troubleshooting.md)
-    several camera models. Please add yours!
+*   [Design documents](design/)
-
+*   [Wiki](https://github.com/scottlamb/moonfire-nvr/wiki) has hardware
-# <a name="help"></a> Getting help and getting involved
+    recommendations and notes on several camera models. Please add yours!
-
-Please email the
-[moonfire-nvr-users](https://groups.google.com/d/forum/moonfire-nvr-users)
-mailing list with questions, or just to say you love/hate the software and
-why. You can also file bugs and feature requests on the
-[github issue tracker](https://github.com/scottlamb/moonfire-nvr/issues).
-
-I'd welcome help with testing, development (in Rust, JavaScript, and HTML),
-user interface/graphic design, and documentation. Please email the mailing
-list if interested. Pull requests are welcome, but I encourage you to discuss
-large changes on the mailing list or in a github issue first to save effort.

design/api.md

@@ -25,13 +25,13 @@ Status: **current**.
 ## Objective
 
 Allow a JavaScript-based web interface to list cameras and view recordings.
+Support external analytics.
 
 In the future, this is likely to be expanded:
 
 *   configuration support
 *   commandline tool over a UNIX-domain socket
     (at least for bootstrapping web authentication)
-*   mobile interface
 
 ## Detailed design