Add a quick plugin development readme

plugin_development.md

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+# Plugin Development
+
+## Overview
+
+## Anatomy of a plugin:
+
+    - plugin_name/
+    -- config.json
+    -- plugin_name.js
+    -- modules_meshcore/ // optional
+    --- plugin_name.js 	// optional
+
+## Plugin Configuration File
+A valid JSON object within a file named `config.json` in the root folder of your project. An example:
+
+    {
+      "name": "Plugin Name",
+      "shortName": "plugin_name",
+      "version": "0.0.0",
+      "author": "Author Name",
+      "description": "Short Description of the plugin",
+      "hasAdminPanel": false,
+      "homepage": "https://www.example.com",
+      "changelogUrl": "https://raw.githubusercontent.com/User/Project/master/changelog.md",
+      "configUrl": "https://raw.githubusercontent.com/User/Project/master/config.json",
+      "downloadUrl": "https://github.com/User/Project/archive/master.zip",
+      "repository": {
+        "type": "git",
+        "url": "https://github.com/User/Project.git"
+      },
+      "versionHistoryUrl": "https://api.github.com/repos/User/Project/tags",
+      "meshCentralCompat": ">0.4.3"
+    }
+    
+## Configuration File Properties
+| Field | Required | Type | Description
+|--|--|--|--|
+| name | Yes | string | a human-readable name for the plugin
+| shortName | Yes | string | an alphanumeric, unique short identifier for the plugin (will be used to access your functions throughout the project
+| version | Yes | string | the current version of the plugin
+| author | No | string | the author's name
+| description | Yes | string | a short, human-readable description of what the plugin does
+| hasAdminPanel | Yes | boolean | `true` or `false`, indicates whether or not the plugin will offer its own administrative interface
+| homepage | Yes | string | the URL of the projects homepage
+| changelogUrl | Yes | string | the URL to the changelog of the project
+| configUrl | Yes | string | the URL to the config.json of the project
+| downloadUrl | Yes | string | the URL to a ZIP of the project (used for installation/upgrades)
+| repository | Yes | JSON object | contains the following attributes
+| repository.type | Yes | string | valid values are `git` and in the future, `npm` will also be supported in the future
+| repository.url | Yes | string | the URL to the project's repository
+| versionHistoryUrl | No | string | the URL to the project's versions/tags
+| meshCentralCompat | Yes | string | the semantic version string of required compatibility with the MeshCentral server
+
+## Plugin Hooks
+These are separated into the following categories depending on the type of functionality the plugin should offer.
+
+- Web UI, to modify the MeshCentral admin interface
+- Back End, to modify core functionality of the server and communicate with the Web UI layer as well as the Mesh Agent (Node) layer to send commands and data
+- Mesh Agent (Node), to introduce functionality to each agent
+
+### Web UI Hooks
+`onDeviceRefeshEnd`: called when a device is selected in the MeshCentral web interface
+`registerPluginTab`: called when a device is selected in the MeshCentral web interface to register a new tab for plugin data, if required
+`onDesktopDisconnect`: called when a remote desktop session is disconnected
+
+#### Exports
+Any function can be exported to the Web UI layer by adding the name of the function to an `exports` array in the plugin object.
+
+### Back End Hooks
+`server_startup`: called once when the server starts (or when the plugin is first installed)
+`hook_agentCoreIsStable`: called once when an agent initially checks in
+`hook_processAgentData`: called each time an agent transmits data back to the server
+
+### Mesh Agent
+Use of the optional file `plugin_name.js` in the optional folder `modules_meshcore` will include the file in the default meshcore file sent to each endpoint. This is useful to add functionality on each of the endpoints.
+
+## Structure
+Much of MeshCentral revolves around returning objects for your structures, and plugins are no different. Within your plugin you can traverse all the way up to the web server and MeshCentral Server classes to access all the functionality those layers provide. This is done by passing the current object to newly created objects, and assigning that reference to a `parent` variable within that object.
+
+
+## Versioning
+Versioning your plugin correctly and consistently is essential to ensure users of your plugin are prompted to upgrade when it is available. Semantic versioning is recommended.
+> Wait, but MeshCentral uses a trailing `-<alpha_char>` for it's versions!
+
+True, but we've made sure that we made special consideration for this in the `meshCentralCompat` check, so you can specify the exact version that you're compatible with. 
+
+## Changelog
+A changelog is highly recommended so that your users know what's changed since their last version.
+
+## Sample Plugin
+[MeshCentral-Sample](https://github.com/ryanblenis/MeshCentral-Sample) is a simple plugin that, upon disconnecting from remote desktop, prompts the user to enter a manual event (note), pre-filled in with the date and timestamp.