In days of yore, the Developer Guide linked to the
IRC page at ceph.io. After the 2021 rewriting of
ceph.io, a new era began, and that page was no
longer easily accessible (it could still be found
at old.ceph.com, but this was deprecated).
Anyway, that IRC information should be included in
the docs. This PR makes sure that the IRC
information is included in the docs.