DOCSP-44006-mongosync-behavior-converting-legacy-indexes (#442) (#443)

* DOCSP-44006-mongosync-behavior-converting-legacy-indexes

* remove reference to valid value

* reword and change title of subsection

* add other mongosync behavior, remove mention of not supporting legacy index vals

Author: amalhotra-mdb

source/reference/mongosync/mongosync-behavior.txt

@@ -133,6 +133,13 @@ Read Preference
 connecting to the source and destination clusters. For more information,
 see :ref:`connections-read-preference`. 
 
+Legacy Index Handling 
+~~~~~~~~~~~~~~~~~~~~~
+
+``mongosync`` rewrites legacy index values, like ``0`` or an empty
+string, to ``1`` on the destination. ``mongosync`` also removes any 
+invalid index options on the destination.
+
 .. _mongosync-considerations:
 
 Considerations for Continuous Sync