Change to using built-in GitHub vulnerability reporting mechanism

SECURITY.md

@@ -6,15 +6,11 @@ Security announcements will be recorded in the [CHANGELOG](CHANGELOG.md).
 
 ## Reporting a Vulnerability
 
-To report a security vulnerability, email
-agithub-security-vulnerability-report-2021@mozilla.com
-
-The members of this security vulnerability report mailing list can be configured
-by Mozilla [here](https://groups.google.com/a/mozilla.com/g/agithub-security-vulnerability-report-2021).
+To report a security vulnerability use the [GitHub Reporting a Security Vulnerability](https://docs.github.com/en/code-security/security-advisories/guidance-on-reporting-and-writing-information-about-vulnerabilities/privately-reporting-a-security-vulnerability) process on the [security tab](https://github.com/mozilla/agithub/security)
 
 ## Supported Versions
 
 agithub is an open source project and all support is community driven. As such
 there are no specific versions which are supported. The newest released
 version which should contain all security fixes can be found on the GitHub
-[releases page](https://github.com/mozilla/agithub/releases)
+[releases page](https://github.com/mozilla/agithub/releases)