Document various Tor failing in the background (i.e. "Proxy server refused connection") errors on Android

Working on #99 (closed), I believe we should document this generic error users see on Tor Browser Android. The documentation can be part of Mobile Tor section on the Manual (maybe under 'Known Issues').

See,

• https://support.torproject.org/connecting/connecting-4/ (We can make this support entry not so desktop specific and link from the Manual as well.)
• tpo/applications/tor-browser#41211 (closed)
• tpo/applications/tor-browser#42714
• tpo/applications/tor-browser#41289 (closed)