Create SECURITY.md

SECURITY.md

+# 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          |
+| ------- | ------------------ |
+| 5.1.x   | :white_check_mark: |
+| 5.0.x   | :x:                |
+| 4.0.x   | :white_check_mark: |
+| < 4.0   | :x:                | -->
+
+## Reporting a Vulnerability
+
+To report a vulnerability, please contact the current maintainer:
+
+https://github.com/scorphus (keybase: https://keybase.io/pablito)
+
+<!-- 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. -->