add note to specify usage in removing shards and link to remove shard tutorial.

Author: Andrew Leung

source/reference/command/movePrimary.txt

@@ -8,7 +8,10 @@ movePrimary
 
    In a :term:`shard cluster`, this command reassigns the database's
    primary shard. The primary shard for a database holds all
-   un-sharded collections in the database.
+   un-sharded collections in the database. :dbcommand:`movePrimary`
+   is an administrative command that is only available for
+   :program:`mongos` instances and is intended to be used when
+   removing a shard from a shard cluster.
 
    :dbcommand:`movePrimary` changes the primary shard for this
    database in the cluster metadata, and migrates all un-sharded
@@ -36,6 +39,4 @@ movePrimary
       :dbcommand:`movePrimary` your shard cluster may have orphaned
       and unreachable data.
 
-   :dbcommand:`movePrimary` is an administrative command that is
-   only available for :program:`mongos` instances.
-
+   .. seealso:: :doc:`/tutorial/remove-shards-from-cluster`