add security policy

SECURITY.md

@@ -0,0 +1,26 @@
+# Security Policy
+
+## Supported Versions
+
+Version | Supported         
+------- | ------------------
+1.2.0 | :white_check_mark:
+1.2.0-beta | :x:
+1.1.0 | :x:
+1.1.0-beta| :x:
+1.0.x | :x:
+
+Only the latest version is supported. If you find a security vulnerability in an eariler version please check it exists in the latest version before reporting.
+
+
+## Reporting a Vulnerability
+
+Please make sure the vulnerability is not already reported by searching existing [issues].
+
+If you're unable to find an existing issue addressing the vulnerability please [open a new issue][new-issue]. 
+Be sure to include a title and clear description and as much relevant information as possible.
+Please tag the issue with the `Security` label.
+
+
+[issues]: https://github.com/irongut/CodeCoverageSummary/issues
+[new-issue]: https://github.com/irongut/CodeCoverageSummary/issues/new