docs: Add Django upgrade to 2.20 release notes (#6999)

Co-authored-by: caitlinwheeless <[email protected]>

Author: caitlinwheeless

docs/source/guide/release_notes/onprem/2.20.0.md

@@ -37,6 +37,9 @@ Optimized the API calls made from the frontend within the members management and
 
 - Updated the default settings for CSRF cookie to be more secure and added an environment setting to control cookie age.
 
+### Breaking changes
+
+This release includes an upgrade to Django 5. As part of this change, Label Studio now requires PostgreSQL version 13+. 
 
 ### Bug fixes