Docs: Add a security policy in SECURITY.md

This is needed so that people know how to report security issues.

Closes gh-2103

Author: mgol

SECURITY.md

@@ -0,0 +1,11 @@
+# Security Policy
+
+## Supported Versions
+
+The [latest released version](https://github.com/jquery/jquery-ui/releases) of jQuery UI is supported.
+
+## Reporting a Vulnerability
+
+Please email [email protected], and we will respond as quickly as possible.
+
+If the vulnerability is considered valid and accepted, a patch will be made for the latest jQuery UI version. If the vulnerability is deemed invalid, no further action is required.