switch to websocket for live stream (#59)

The multipart stream / hanging GET approach worked in a prototype for a
single stream, but Chrome has a per-host limit of six connections. If I
try streaming all my cameras at once, I hit that limit. I can't open all
the streams, much less additional connections to load init segments and
such. Websockets apparently has a much higher limit of 256.

guide/secure.md

@@ -198,6 +198,11 @@ upstream moonfire {
     server 127.0.0.1:8080;
 }
 
+map $http_upgrade $connection_upgrade {
+    default Upgrade;
+    ''      close;
+}
+
 server {
     root /var/www/html;
     index index.html index.htm index.nginx-debian.html;
@@ -209,6 +214,10 @@ server {
         # try_files $uri $uri/ =404;
     }
 
+    proxy_http_version 1.1;
+    proxy_set_header Upgrade $http_upgrade;
+    proxy_set_header Connection $connection_upgrade;
+
     proxy_set_header X-Forwarded-Proto $scheme;
     proxy_set_header X-Real-IP $remote_addr;
     proxy_set_header Host $http_host;
@@ -256,5 +265,9 @@ Login with the credentials you added through `moonfire-nvr config` in the
 [previous guide](install.md). You should see your username and "logout" in the
 upper-right corner of the web interface.
 
+Also try the live streaming feature, which requires WebSockets. The nginx
+configuration above includes sections derived from nginx's [NGINX as a
+WebSocket Proxy](https://www.nginx.com/blog/websocket-nginx/) doc.
+
 If it doesn't work as expected, re-read this guide, then open an issue on
 github for help.