Update whats-new-docs.md

Author: csmulligan

articles/active-directory/external-identities/customers/whats-new-docs.md

@@ -17,6 +17,8 @@ Welcome to what's new in Azure Active Directory for customers documentation. Thi
 
 ## September 2023
 
+This month, we renamed Azure Active Directory (Azure AD) to Microsoft Entra ID. For more information about the rebranding, see the [New name for Azure Active Directory](/azure/active-directory/fundamentals/new-name) article.
+
 ### Updated articles
 
 - [Quickstart: Get started with our guide to run a sample app and sign in your users (preview)](quickstart-get-started-guide.md) Start the guide updates