minor: fixing formating error in moveChunk documents.

Author: Sam Kleinman

source/reference/command/moveChunk.txt

@@ -10,16 +10,18 @@ moveChunk
    sharding. Use the :method:`sh.moveChunk()` helper in the
    :program:`mongo` shell for manual chunk migrations.
 
-   :option _secondaryThrottle: ``false`` by default. If ``true``
-                               during chunk migrations when a
-                               :term:`shard` hosted by a
-                               :term:`replica set`, the
-                               :program:`mongod` will wait until the
-                               :term:`secondary` members replicate the
-                               migration operations continuing to
-                               migrate chunk data.
+   :option _secondaryThrottle: Set to ``false`` by default. Provides
+                               :ref:`write concern <write-concern>`
+                               support for chunk migrations.
 
-    For details on chunk migrations see the :ref:`Chunk Migration
-    <sharding-chunk-migration>` section.
+   If ``_secondaryThrottle`` is set to ``true``, during chunk
+   migrations when a :term:`shard` hosted by a :term:`replica set`,
+   the :program:`mongod` will wait until the :term:`secondary` members
+   replicate the migration operations continuing to migrate chunk
+   data. In the balancer configuration, the ``replThrottle``
+   configuration provides ``_secondaryThrottle`` behavior.
+
+   For details on chunk migrations see the :ref:`Chunk Migration
+   <sharding-chunk-migration>` section.
 
    .. admin-only