.doap file is missing

[Neustradamus]

Dear @xmppjs team,

Can you add the XEP-0453: DOAP usage in XMPP support:

• https://xmpp.org/extensions/xep-0453.html

It permits to update easily and to specify all that it is supported by the project on xmpp.org.

Linked to:

• XEPs and RFCs support page with version #531

[sonnyp]

PR welcome :)