Update the Documentation link from 2.2 -> 3.0
Helpful for newbies.
Please refer to our hosted documentation here: http://docs.ceph.com/ceph-ansible/master/
You can view documentation for our ``stable-*`` branches by substituting ``master`` in the link
-above for the name of the branch. For example: http://docs.ceph.com/ceph-ansible/stable-2.2/
+above for the name of the branch. For example: http://docs.ceph.com/ceph-ansible/stable-3.0/