Update security policy

Author: tallclair

SECURITY.md

@@ -1,14 +1,22 @@
 # Security Policy
 
-## Supported Versions
+## Security Announcements
 
-Information about supported Kubernetes versions can be found on the
-[Kubernetes version and version skew support policy] page on the Kubernetes website.
+Join the [kubernetes-security-announce] group for security and vulnerability announcements.
+
+You can also subscribe to an RSS feed of the above using [this link][kubernetes-security-announce-rss].
 
 ## Reporting a Vulnerability
 
 Instructions for reporting a vulnerability can be found on the
 [Kubernetes Security and Disclosure Information] page.
 
+## Supported Versions
+
+Information about supported Kubernetes versions can be found on the
+[Kubernetes version and version skew support policy] page on the Kubernetes website.
+
+[kubernetes-security-announce]: https://groups.google.com/forum/#!forum/kubernetes-security-announce
+[kubernetes-security-announce-rss]: https://groups.google.com/forum/feed/kubernetes-security-announce/msgs/rss_v2_0.xml?num=50
 [Kubernetes version and version skew support policy]: https://kubernetes.io/docs/setup/release/version-skew-policy/#supported-versions
 [Kubernetes Security and Disclosure Information]: https://kubernetes.io/docs/reference/issues-security/security/#report-a-vulnerability