DOCS-515 corrections for secondaryThrottle

Author: Sam Kleinman

source/core/sharding-internals.txt

@@ -493,5 +493,5 @@ All chunk migrations use the following procedure:
    its copy of documents from the migrated chunk.
 
 When the ``_secondaryThrottle`` is ``true`` for :dbcommand:`moveChunk`
-or the :term:`balancer`, MongoDB ensures :term:`secondary` members
-have replicated changes before allowing new chunk migrations.
+or the :term:`balancer`, MongoDB ensure that *one* :term:`secondary`
+member has replicated changes before allowing new chunk migrations.

source/reference/command/moveChunk.txt

@@ -38,17 +38,17 @@ moveChunk
    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.
+   data. You may also configure ``_secondaryThrottle`` in the balancer
+   configuration.
 
    Use the :method:`sh.moveChunk()` helper in the :program:`mongo`
    shell to migrate chunks manually.
 
    The :ref:`chunk migration <sharding-chunk-migration>` section
    describes how chunks move between shards on MongoDB.
 
-   :dbcommand:`moveChunk` will return the following if the
-   chunk to be moved is in use by another :term:`cursor`:
+   :dbcommand:`moveChunk` will return the following if another cursor
+   is using the chunk you are moving:
 
    .. code-block:: none