Mention CephFS deprection in the user doc to notify the users.

The CephFS intree storage driver  is getting deprecated in kubernetes
release 1.28 and users have to be notified about the same.

Author: humblec

volumes/cephfs/README.md

@@ -1,5 +1,11 @@
 # How to Use it?
 
+NOTE: CephFS storage driver ( `kubernetes.io/cephfs`) has been
+deprecated in kubernetes 1.28 release and will be in removed in subsequent
+releases. The CSI driver for CephFS (https://github.com/ceph/ceph-csi)
+is available for long time now which can be an alternative option for the
+users want to use CephFS volumes in their clusters.
+
 Install Ceph on the Kubernetes host. For example, on Fedora 21
 
     # yum -y install ceph