Indication of the XEP version supported

[Neustradamus]

Can you add in the README, the current XEP-0280 version supported (XEP-XXXX v1.2)?

Examples:

• https://metronome.im/supported-xeps-list
• https://dev.gajim.org/gajim/gajim/wikis/help/gajimxepsupport
• https://github.com/jappix/jappix/blob/master/PROTOCOL.md

[Neustradamus]

@gkdr: Thanks :)