Add release notes for ##12521

docs/releases/6.3.md

@@ -118,6 +118,7 @@ This feature was developed by Bart Cieliński, alexkiro, and Sage Abdullah.
 ### Documentation
 
  * Upgrade Sphinx to 7.3 (Matt Westcott)
+ * Upgrade sphinx-wagtail-theme to v6.4.0, with a new search integration and Read the Docs Addons bug fixes (Thibaud Colas)
  * Document how to [customize date/time format settings](wagtail_date_time_formats) (Vince Salvino)
  * Create a new documentation section for [deployment](deployment_guide) and move `fly.io` deployment from the tutorial to this section (Vince Salvino)
  * Clarify process for [UserViewSet customization](custom_userviewset) (Sage Abdullah)