Add security policy (#116)

* Add security policy

* Reference wiki version map instead of concrete table

Avoids duplicating version support info that is already
maintained in the wiki, reducing maintenance burden.

Author: jamisonbryant

.github/SECURITY.md

@@ -0,0 +1,24 @@
+# Security Policy
+
+## Supported Versions
+
+Security fixes are applied to all active versions listed in the
+[version map](https://github.com/cakephp/twig-view/wiki#cakephp-version-map).
+Versions marked as EOL no longer receive fixes.
+
+## Reporting a Vulnerability
+
+If you've found a security issue in the CakePHP TwigView plugin, please use the following procedure
+instead of the normal bug reporting system. Instead of using the bug tracker,
+or one of the support forums please send an email to security [at] cakephp.org. Emails
+sent to this address go to the CakePHP core team on a private mailing list.
+
+For each report, we try to first confirm the vulnerability. Once confirmed,
+the CakePHP team will take the following actions:
+
+* Acknowledge to the reporter that we've received the issue, and are
+  working on a fix. We ask that the reporter keep the issue confidential until we announce it.
+* Get a fix/patch prepared.
+* Prepare a post describing the vulnerability, and the possible exploits.
+* Release new versions of all affected versions.
+* Prominently feature the problem in the release announcement