DOCSP-40286 update wording (#353)

Author: jocelyn-mendez1

source/multiple-mongosyncs.txt

@@ -21,7 +21,7 @@ source cluster.
 .. important::
 
    When the source or destination cluster is a sharded cluster, stop the
-   balancer and don't run the :dbcommand:`moveChunk` or
+   balancer on both clusters and don't run the :dbcommand:`moveChunk` or
    :dbcommand:`moveRange` commands for the entire lifetime of the
    migration. To stop the balancer, run the :dbcommand:`balancerStop`
    command and wait for the command to complete.