docs(security): add SECURITY.md

Inspired by https://github.com/fb55/htmlparser2/blob/v6.0.0/SECURITY.md

Author: remarkablemark

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+Only the current version is supported. Please make sure to update to the latest release.
+
+## Reporting a Vulnerability
+
+To report a security vulnerability, please use the [Tidelift security contact](https://tidelift.com/security).
+Tidelift will coordinate the fix and disclosure.