ceph: update snapshot doc as per beta version
ceph: update snapshot doc as per beta version

Updated the snapshot usage doc as per new
snapshot beta version.

Signed-off-by: Madhu Rajanna <60fbf37a92c2a0908e31296d18dadbec5a4dae17@gmail.com>

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