Add usage docs

[ikatson]

There were a lot of new features added, some hidden / not obvious. Update usage docs, maybe create a separate guide for that

E.g.

• [ ] socks
• [ ] UpnP
• [ ] watching a directory for torrent files
• [ ] http auth
• [ ] upload / download limits
• [ ] adding torrents using just infohash
• [ ] playlists
• [ ] fastresume
• [ ] document IPv6 support, maybe test if it actually works? DHT, peer connections, upnp etc.

BEPs:

• [ ] padding files
• [ ] pex
• [ ] bep 53 ( select only)

HTTP endpoints:

• [ ] stats, all stats
• [ ] all the other endpoints

Maybe update / include the list of supported BEPs also