Add blurb to 5.0 release notes for movePrimary error message

Author: ianf-mongodb

source/release-notes/5.0.txt

@@ -460,6 +460,13 @@ the ``"disabled"`` option.
 Starting in MongoDB 5.0, you can use the :dbcommand:`renameCollection`
 command to change the name of a sharded collection.
 
+``movePrimary`` Error Message For Writes During Operation
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting in MongoDB 5.0, when using the :dbcommand:`movePrimary` command
+to remove a shard from a :ref:`sharded cluster <sharded-cluster>`, 
+writes to the original shard will generate an error message.
+
 .. _5.0-rel-notes-shell:
 
 Shell Changes