ceph: document unique crush name requirement
ceph: document unique crush name requirement

CRUSH hierarchy requires unique names at each location.

Signed-off-by: Travis Nielsen <a8b474fdb3f77f44446f0ab9ddca8147b09b3a9e@redhat.com>

rook/rook,rook/nfs,rook/nfs,rook/nfs,rook/rook,rook/rook,rook/rook,rook/rook