CONTRIBUTING.md in paperclip-4.3.7 vs CONTRIBUTING.md in paperclip-5.0.0.beta1

@@ -1,8 +1,13 @@
 Contributing
 ============
 
-We love pull requests. Here's a quick guide:
+We love pull requests from everyone. By participating in this project, you agree
+to abide by the thoughtbot [code of conduct].
+
+[code of conduct]: https://thoughtbot.com/open-source-code-of-conduct
+
+Here's a quick guide for contributing:
 
 1. Fork the repo.
 
 2. Run the tests. We only take pull requests with passing tests, and it's great
 to know that you have a clean slate: `bundle && bundle exec rake`