adds a note about default chunk size increase to Release Notes (#224)

Author: jmd-mongo

source/release-notes/5.2.txt

@@ -76,6 +76,13 @@ started is included in the:
 
 - :data:`config.mongos` collection
 
+Default Chunk Size Increased from 64 MB to 128 MB 
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Starting in MongoDB 5.2, the 
+:ref:`default chunk size <sharding-chunk-size>` is 128 megabytes. In 
+earlier versions of MongoDB, the default chunk size is 64 megabytes.
+
 .. _5.2-rel-notes-general:
 
 General Improvements