DOCSP-1505: added language to clarify selected tab

Signed-off-by: kay <[email protected]>

Author: skerschb

source/tutorial/change-streams-example.txt

@@ -14,7 +14,7 @@ Change Stream Examples
    Change streams are available for replica sets or sharded clusters with replica set
    shards. You cannot open a change stream against a standalone :binary:`~bin.mongod`. 
    For a sharded cluster, you must issue the open change stream operation against
-   the :binary:`~bin.mongos`.
+   the :binary:`~bin.mongos`. 
 
    The replica set or the sharded cluster must use: