DOCS-15383 add Behavior section to configureColBal (#1222)

* DOCS-15383 add Behavior section to configureColBal

* chunkSize

* monospace

* CR1 Feedback

* fix header lengths

* TR1 Feedback

* add ref to chuck size tutorial

* on

Author: ianf-mongodb

source/reference/command/configureCollectionBalancing.txt

@@ -65,11 +65,31 @@ Command Fields
 For more information, see :ref:`Data Partitioning with Chunks
 <sharding-data-partitioning>`.
 
+Behavior
+--------
+
+No Collection ``chunkSize`` Specified
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you do not specify ``chunkSize`` for a collection and no custom size 
+has been set previously, the global default ``chunkSize`` is 
+used for balancing.
+
+Specifying ``chunkSize: 0``
+~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+If you use :dbcommand:`configureCollectionBalancing` with
+``chunkSize: 0``, the per-collection ``chunkSize`` is reset and the 
+global default ``chunkSize`` is used for balancing.
+
+For more information on configuring default ``chunkSize``,
+see :ref:`tutorial-modifying-chunk-size`.
+
 Examples
-----------
+--------
 
 Configure Chunk Size
-~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~
 
 To change the chunk size for a sharded collection, use
 the ``chunkSize`` option:
@@ -95,7 +115,7 @@ Use this command to change the chunk size for the given collection.
 For more information, see :ref:`Chunk Size <sharding-chunk-size>`.
 
 Defragment Collections
-~~~~~~~~~~~~~~~~~~~~~~~~
+~~~~~~~~~~~~~~~~~~~~~~
 
 To tell the balancer to defragment a sharded collection, use the
 ``defragmentCollection`` option:

source/tutorial/modify-chunk-size-in-sharded-cluster.txt

@@ -1,3 +1,5 @@
+.. _tutorial-modifying-chunk-size:
+
 ======================================
 Modify Chunk Size in a Sharded Cluster
 ======================================