Add security policy

Add security.md with supported versions and vulnerability reporting
instructions via GitHub Security Advisories.

Author: costajohnt

security.md

@@ -0,0 +1,16 @@
+# Security Policy
+
+## Supported Versions
+
+| Version | Supported |
+| ------- | --------- |
+| 6.x     | ✅        |
+| < 6     | ❌        |
+
+## Reporting a Vulnerability
+
+To report a security vulnerability, please use the [GitHub Security Advisory](https://github.com/vadimdemedes/ink/security/advisories/new) feature, which allows for private disclosure.
+
+Please do **not** open a public issue for security vulnerabilities.
+
+You should receive a response within a few days. If the vulnerability is confirmed, a patch will be released as soon as possible.