(DOCS-14803): Clarification for range deletes

Author: jeff-allen-mongo

source/core/sharding-balancer-administration.txt

@@ -329,6 +329,12 @@ with :parameter:`rangeDeleterBatchSize` and
   :parameter:`rangeDeleterBatchDelayMS` above the current default of
   ``20`` milliseconds.
 
+.. note::
+
+   If there are ongoing read operations or open cursors on the
+   collection targeted for deletes, range deletion processes may
+   not proceed.
+
 .. _sharding-shard-size:
 
 Shard Size