add whats-new entry

Author: PatrickFarley

articles/ai-services/content-safety/whats-new.md

@@ -16,6 +16,15 @@ ms.author: pafarley
 
 Learn what's new in the service. These items might be release notes, videos, blog posts, and other types of information. Bookmark this page to stay up to date with new features, enhancements, fixes, and documentation updates.
 
+## May 2024
+
+### Custom category support in Content Safety moderation APIs
+
+The custom categories API lets you create and train your own custom content categories and scan text and images for matches. See [Custom categories](./concepts/custom-categories.md) to learn more.
+
+### Incident response API
+
+The incident response API lets you quickly define emerging harmful content patterns and scan text and images for matches. See [Incident response](./concepts/incident-response.md) to learn more.
 
 ## March 2024