Add notes on git organization and PR process

CONTRIBUTING.md

@@ -1,3 +1,20 @@
+## Git organization and Pull Request process
+
+This project uses a Gitflow-like organization for code:
+
+* The `master` branch represents a stable version of the project at any given time.
+* Releases are tags on the `master` branch.
+* All features and bug fixes are performed against the `develop` branch.
+* New features are allocated their own branch based on the `develop` branch, and pull requests are made from the new feature branch to the `develop` branch.
+
+Developers who wish to submit a pull request should perform the following protocol:
+
+1. Fork the project on GitHub
+2. Create a special-purpose branch from the `develop` branch, e.g. 'fix-filevault' or 'disable-apple-mail'
+3. Implement the changes in the branch
+4. Follow the guidelines in the sections below depending on whether you are modifying configuration checks, Python code, or any combination therefore
+5. Make a pull request from your feature branch to the `develop` branch. 
+
 ## Modifying default configuration checks
 
 All default configuration checks -- that is, the set of configurations that will be checked and fixed if insecure when the user runs `app.py` -- are expressed in the `osx-config.hjson` file. This file is written in [Hjson](http://hjson.org/) to make it easy to read and modify.