docs: update doc
docs: update doc

- stable-2.1 and stable-2.2 shouldn't be referenced anymore.
- add stable-3.1 branch reference
- update the differents ansible version supported

Signed-off-by: Guillaume Abrioux <30a9df5a0293a6108675377fa1673f7aa713f915@redhat.com>

font/ceph-ansible,fgal/ceph-ansible,font/ceph-ansible,ceph/ceph-ansible,fgal/ceph-ansible,ceph/ceph-ansible