Add CONTRIBUTING.md to the repo

Provide some guidelines on contributions and link to the document from the
About page on the website.

CONTRIBUTING.md

@@ -0,0 +1,48 @@
+# Contributing
+
+Thanks for your interest in contributing to the Open Policy Agent (OPA) project!
+
+# Where to start?
+
+If you have questions, comments, or requests feel free to post on the mailing list or
+create an issue on GitHub.
+
+If you want to contribute code and you are new to the Go programming language, check out
+the [Development](http://openpolicyagent.org/docs/development.html) reference for help getting started.
+
+We currently welcome contributions of all kinds. For example:
+
+- Development of features, bug fixes, and other improvements.
+- Documentation including reference material and examples.
+- Bug and feature reports.
+
+# Contribution process
+
+Small bug fixes (or other small improvements) can be submitted directly via a Pull Request on GitHub.
+You can expect at least one of the OPA maintainers to respond quickly.
+
+Before submitting large changes, please open an issue on GitHub outlining:
+
+- The use case that your changes are applicable to.
+- Steps to reproduce the issue(s) if applicable.
+- Detailed description of what your changes would entail.
+- Alternative solutions or approaches if applicable.
+
+Use your judgement about what constitutes a large change. If you aren't sure, send a message to the
+mailing list or submit an issue on GitHub.
+
+## Code Contributions
+
+If are contributing code, please consider the following:
+
+- Most changes should be accompanied with tests.
+- Commit messages should explain *why* the changes were made and should probably look like this:
+
+        Description of the change in 50 characters or less
+
+        More detail on what was changed. Provide some background on the issue
+        and describe how the changes address the issue. Feel free to use multiple
+        paragraphs but please keep each line under 72 characters or so.
+
+- Related commits must be squashed before they are merged.
+- All tests must pass and there must be no warnings from the `make check` target.

docs/about.md

@@ -5,11 +5,22 @@ header_title: About
 show_in_header: true
 ---
 
+About
+=====
+
+The Open Policy Agent (OPA) project is under active development.
+
+For information on contributing to OPA, see the [CONTRIBUTING.md](https://github.com/open-policy-agent/opa/master/CONTRIBUTING.md) file in the repository.
+
+Contact
+-------
+
+- Bugs: [Github Issues](https://github.com/open-policy-agent/opa/issues) 
+- Features: [Github Issues](https://github.com/open-policy-agent/opa/issues)
+- Discussions: [Google Groups](https://groups.google.com/forum/?hl=en#!forum/open-policy-agent)
+
 Project Information
 -------------------
 
 - License: [Apache Version 2.0](https://raw.githubusercontent.com/open-policy-agent/opa/master/LICENSE)
-- Bugs: [Github Issues](https://github.com/open-policy-agent/opa/issues) 
-- Features: [Github Issues](https://github.com/open-policy-agent/opa/issues)
-- Discussions: [Google Groups](https://groups.google.com/forum/?hl=en#!forum/open-policy-agent)
 - Continuous Integration: [![Build Status](https://travis-ci.org/open-policy-agent/opa.svg?branch=master)](https://travis-ci.org/open-policy-agent/opa)