(DOCSP-15594): Clarify version for concurrent shard removal

Author: jeff-allen-mongo

source/reference/command/removeShard.txt

@@ -34,6 +34,15 @@ You can only remove one shard at a time.
 :dbcommand:`removeShard` returns an error if an existing
 :dbcommand:`removeShard` operation is in progress.
 
+Concurrent ``removeShard`` Operations
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting in MongoDB 4.2.1, you can have more than one
+:dbcommand:`removeShard` operation in progress.
+
+In MongoDB 4.2.0 and earlier, :dbcommand:`removeShard` returns an error
+if another :dbcommand:`removeShard` operation is in progress.
+
 Access Requirements
 ~~~~~~~~~~~~~~~~~~~