docs: update security policy for OWASP Java Encoder

Author: jeremylong

SECURITY.md

@@ -0,0 +1,14 @@
+# Security Policy
+
+## Supported Versions
+
+Only the currently released version of the OWASP Java Encoder is supported.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 1.3.1   | :white_check_mark: |
+| < 1.3.1 | :x:                |
+
+## Reporting a Vulnerability
+
+If you suspect that there is a vulnerability, please open an issue.