Add consistent SECURITY.md (#14639)

SECURITY.md

@@ -1,3 +1,7 @@
-# Knative security policy
+# Knative Security Policy
 
-See https://github.com/knative/community/blob/main/SECURITY.md for the Knative security policy.
+We're extremely grateful for security researchers and users that report vulnerabilities to the Knative Open Source Community. All reports are thoroughly investigated by a set of community volunteers.
+
+To make a report, please email the private [email protected] list with the security details and the details expected for all Knative bug reports.
+
+See [Knative Security and Disclosure Information](https://knative.dev/docs/reference/security/) for more details.