The source project of this merge request has been removed.
Clarify differences between Matrix and XMPP
First, replace Jabber with XMPP. The protocol was named Jabber in the first place, but has been renamed to XMPP since then.
Also, make it clear that XMPP is also federated, and that federation is not the reason why rooms are duplicated, this is just a particularity of Matrix compared with XMPP.