dm: add dm-clone to the documentation index

Fixes: 7431b7835f554 ("dm: add clone target")
Signed-off-by: Diego Calleja <diegocg@gmail.com>
Signed-off-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
1 file changed