Create SECURITY.md (#21)

Create security policy.

Author: s0

SECURITY.md

@@ -0,0 +1,11 @@
+# Security Policy
+
+## Supported Versions
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 1.x.x   | :white_check_mark: |
+
+## Reporting a Vulnerability
+
+Please select "Report a Vulnerability" on the [Security Tab](https://github.com/s0/ghcommit/security). We will investigate all legitimate reports and do our best to quickly fix the problem.