Create SECURITY.md

Could the maintainer please create a SECURITY.md and publish a security policy in Github?  Or provide the information and I'm happy to author and create a PR.

SECURITY.md

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+# Security Policy
+TODO:  Publish a security policy so users know the process for reporting vulnerabilities and expectations on fixes.
+
+## Supported Versions
+
+Use this section to tell people about which versions of your project are
+currently being supported with security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 5.1.x   | :white_check_mark: |
+| 5.0.x   | :x:                |
+| 4.0.x   | :white_check_mark: |
+| < 4.0   | :x:                |
+
+## Reporting a Vulnerability
+
+Use this section to tell people how to report a vulnerability.
+
+Tell them where to go, how often they can expect to get an update on a
+reported vulnerability, what to expect if the vulnerability is accepted or
+declined, etc.