Update whats-new.md

adding link to MSEM what's new

Author: DebLanger

unified-secops-platform/whats-new.md

@@ -48,5 +48,6 @@ For more information on what's new with other Microsoft Defender security produc
 - [What's new in Microsoft Defender for Endpoint](/defender-endpoint/whats-new-in-microsoft-defender-endpoint)
 - [What's new in Microsoft Defender for Identity](/defender-for-identity/whats-new)
 - [What's new in Microsoft Defender for Cloud Apps](/cloud-app-security/release-notes)
+- [What's new in Microsoft Security Exposure Management](/security-exposure-management/whats-new)
 
 You can also get product updates and important notifications through the [message center](https://admin.microsoft.com/Adminportal/Home#/MessageCenter).