move release note

Author: rachel-mack

source/data-formats/serialization.txt

@@ -227,6 +227,8 @@ encode defaults:
    :end-before: end-codec
    :dedent:
 
+.. _kotlin-sync-serialization-snake-case-eg:
+
 Enforcing Snake Case Naming Example
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 

source/whats-new.txt

@@ -29,6 +29,10 @@ What's New in 5.4
 The 5.4 driver release includes the following changes, fixes,
 and features:
 
+- Adds support for converting field names to snake case during serialization. To
+  learn more, see the :ref:`kotlin-sync-serialization-snake-case-eg` on the
+  Serialization page.
+
 .. sharedinclude:: dbx/jvm/v5.4-wn-items.rst
 
    .. replacement:: install-bom-link