Updated CONTRIBUTING.md file

CONTRIBUTING.md

@@ -1,17 +1,30 @@
+How to contribute
+================
+We welcome contributions to Concordion extensions. This document lists the guidelines for contributing.
+
+Proposing a change
+-----------------------------
+Firstly, you should create an issue for your enhancement request. You may also want to discuss the change with the [concordion-dev list](https://groups.google.com/forum/#!forum/concordion-dev) before implementation.
+
+New feature proposals should be described with acceptance tests. For features not yet implemented, please add the `@Unimplemented` annotation.
+
+Implementing a change
+----------------------------------
+Concordion uses a "Fork & Pull" model for collaborative development. If you have changes that you would like us to consider for introduction to Concordion, you will need to:
+ 1. [fork](https://help.github.com/articles/fork-a-repo) the repository, 
+ 1. commit and push your changes to your forked project, and 
+ 1. send us a [pull request](https://help.github.com/articles/using-pull-requests) referencing the URL of the issue that you created.
+
+
 Development Rules
 -----------------
-
 * Don't break existing behaviour. Backward compatibility is extremely important.
-
 * New feature proposals should be described with acceptance tests and discussed with the [concordion-dev list](https://groups.google.com/forum/#!forum/concordion-dev) before implementation.
-
 * Follow the style and conventions of the existing code (basically Sun's conventions). In particular:
   - Use 4 spaces (not tabs) 
   - Line width of 120 characters
   - Always use braces after "if" statements.
-
 * All code changes should have automated tests of some sort.
-
 * Never check a failing test into the repository. (Though you can check-in unimplemented acceptance test HTML for new feature ideas). 
 
 Building