docs: Mention github security advisories tool in security policy (#2807)

* docs: Mention github security advisories tool in security policy

* Mention google groups message in security policy for reporting vulnerability

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Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

SECURITY.md

@@ -2,8 +2,12 @@
 
 ## Reporting a Vulnerability
 
-To report a security problem in Kanister, please contact the maintainers listed
-in the [MAINTAINERS.md](MAINTAINERS.md) file.
+Current known vulnerabilities are listed in the
+[github security advisories](https://github.com/kanisterio/kanister/security/advisories) section for the repo.
+You can report a new vulnerability using
+[Report a vulnerability](https://github.com/kanisterio/kanister/security/advisories/new) tool.
+
+Alternatively you can report it via kanisterio google group "Contact owners and managers" button: https://groups.google.com/g/kanisterio/about
 
 The maintainers will help diagnose the severity of the issue and determine how
 to address the issue. Issues deemed to be non-critical will be filed as GitHub
@@ -15,7 +19,7 @@ as possible. The maintainers will then coordinate a release date with you.
 When serious security problems in Kanister are discovered and corrected, the
 maintainers issue a security advisory, describing the problem and containing a
 pointer to the fix. These will be announced on the Kanister's mailing list and
-websites.
+websites and be visible in [github security advisories](https://github.com/kanisterio/kanister/security/advisories).
 
 Security issues are fixed as soon as possible, and the fixes are propagated to
 the stable branches as fast as possible. However, when a vulnerability is found