feat(securitry): create security policy

A simple template.

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+Use this section to tell people about which versions of your project are
+currently being supported with security updates.
+
+| Version | Supported          | Notes |
+| ------- | ------------------ | --- |
+| latest  | :white_check_mark: | This will always be supported. |
+| Older   | :x:                | This does not mean it has flaw, just no support. |
+
+## 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.