Update release notes.

docs/topics/release-notes.md

@@ -19,10 +19,13 @@ Major version numbers (x.0.0) are reserved for project milestones.  No major poi
 ### Master
 
 * Deprecate django.utils.simplejson in favor of Python 2.6's built-in json module.
+* Bugfix: PK fields now only default to `read_only=True` if they are an AutoField or if `editable=False`.
 * Bugfix: Validation errors instead of exceptions when serializers receive incorrect types.
 * Bugfix: Validation errors instead of exceptions when related fields receive incorrect types.
 * Bugfix: Handle ObjectDoesNotExist exception when serializing null reverse one-to-one
 
+**Note**: If you are using auto UUID fields as your primary keys, you probably want to make sure that the model fields correctly set `editable=False`.
+
 ### 2.1.15
 
 **Date**: 3rd Jan 2013