Update SECURITY.md (#2)

* Update SECURITY.md

Changed the link to the Umrbaco security policies and added a link so people could find a way to get notified when we have taken action on something related to security.

* Add section for security advisories.

---------

Co-authored-by: Sebastiaan Janssen <[email protected]>

Author: Abdjulaziz

.github/SECURITY.md

@@ -4,6 +4,10 @@
 
 Please report any vulnerabilities to [email protected]
 
-Read more about [Umbraco's security policies](https://umbraco.com/about-us/trust-center/security-and-umbraco/how-to-report-a-vulnerability-in-umbraco/).
+Read more about [Umbraco's security policies](https://umbraco.com/trust-center/security-and-umbraco/how-to-report-a-vulnerability-in-umbraco/).
 
 You can expect to hear back from us within 48 hours.
+
+## Security advisories
+
+You can sign up for [Umbraco security advisories & notifications](https://umbraco.activehosted.com/f/33)