DOCSP-46629-replSetResizeOplog-unsupported-Atlas (#558)

* DOCSP-46629-replSetResizeOplog-unsupported-Atlas

* indent

* reviewer changes

* undo some changes

Author: amalhotra-mdb

source/reference/oplog-sizing.txt

@@ -63,6 +63,12 @@ Monitor oplog Size Needed for Initial Sync
       - Increase the ``oplog`` window. Use :dbcommand:`replSetResizeOplog`
         to set ``minRetentionHours`` greater than the current ``oplog`` 
         window.
+
+        .. note:: 
+
+           :dbcommand:`replSetResizeOplog` is unsupported in Atlas. To resize 
+           the oplog in Atlas, see :ref:`set-oplog-min-window`.    
+
       - Scale up the ``mongosync`` instance. Add CPU or memory to scale
         up the ``mongosync`` node so that it has a higher copy rate.