ovsdb.7.rst: some corrections in ovsdb-client usage.
1. Correct typo where it should be ovsdb-client backup vs ovsdb-tool backup.
2. Update for which case will ovsdb-client not work.
Acked-by: Han Zhou
@@ -509,8 +509,10 @@ Changing Database Service Model
-------------------------------
Use ``ovsdb-tool create-cluster`` to create a clustered database from the
-contents of a standalone database. Use ``ovsdb-tool backup`` to create a
-standalone database from the contents of a clustered database.
+contents of a standalone database. Use ``ovsdb-client backup`` to create a
+standalone database from the contents of a running clustered database.
+When the cluster is down and cannot be revived, ``ovsdb-client backup`` will
+not work.
Upgrading or Downgrading a Database
-----------------------------------
