Create SECURITY.md

Author: Link-

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+Only the versions in the table below will receive security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 2.x.x   | :white_check_mark: |
+
+## Reporting a Vulnerability
+
+Use the [private vulnerability reporting feature](https://github.com/Link-/gh-token/security/advisories) to report security problems.