Documentation update: Apache configuration

[rahra]

To use the Apache HTTP server as a reverse proxy, here's how-to:

1. Setup Apache and SSL as usual.
2. Add modules proxy_http, proxy_http2, proxy_wstunnel, and headers (with a2enmod <mod>).
3. In your VirtualHost config add the following 2 lines:

ProxyPass / http://localhost:8000/ upgrade=websocket
RequestHeader set Origin "http://localhost:8000"