DOCSP-40105-storageEngine-limitation (#348)

Author: ajhuh-mdb

source/reference/limitations.txt

@@ -59,6 +59,8 @@ General Limitations
 - ``mongosync`` does not support syncing 
   `Atlas Search Indexes
   <https://www.mongodb.com/docs/atlas/atlas-search/create-index/>`__.
+- ``mongosync`` only supports clusters that use the :ref:`WiredTiger 
+  <storage-wiredtiger>` storage engine.
 
 MongoDB Community Edition
 -------------------------