Make sample config just have the HS config

The other options are things people usually won't need or want to
set, so just keep it to the basics.

 * Rename config sample to match element-web
 * Update / simplify build instructions
 * Rename nginx config file to differentiate it from EC config

.env.example

@@ -5,7 +5,6 @@
 ####
 
 # Used for determining the homeserver to use for short urls etc.
-# VITE_DEFAULT_HOMESERVER=http://localhost:8008
 # VITE_FALLBACK_STUN_ALLOWED=false
 
 # VITE_CUSTOM_THEME=true