doc: correct kubernetes version for snap and clone
doc: correct kubernetes version for snap and clone

Corrected the required kubernetes version for rbd
snapshot and clone in README.

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

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi