Define security policy and contact method (#293)

Fixes #229

SECURITY.md

@@ -0,0 +1,16 @@
+# Security Policy
+
+## Supported Versions
+
+Latest major version of Lefthook is being supported with security updates.
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 1.x     | :white_check_mark: |
+| 0.x     | :x:                |
+
+## Reporting a Vulnerability
+
+If you have found a security issue in Lefthook, please **do not** create a new issue in the GitHub repository. Instead, please send an email to [lefthook@evilmartians.com](mailto:lefthook@evilmartians.com?subject=Lefthook%3A%20security%20issue) describing what the problem is and how to reproduce it. We will get in touch with you!
+
+Please note that Lefthook, as a CLI tool, executes arbitrary commands and scripts from its configuration file by design. This is intended behavior. Feel free to join the discussion on [issue #229](https://github.com/evilmartians/lefthook/issues/229).