Adding contributing file

CONTRIBUTING.md

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+# How to contribute
+
+Contributing to AsgardCMS is fairly straitforward. The easiest way is listed below. 
+
+Please note AsgardCMS follows **[PSR-1](http://www.php-fig.org/psr/psr-1/)** and **[PSR-2](http://www.php-fig.org/psr/psr-2/)**. Please make sure your code follows those standards.
+
+You can use a great tool : **[PHP-CS-Fixer](https://github.com/FriendsOfPHP/PHP-CS-Fixer)** to make sure everything is following the correct coding style.
+
+Install it globally and run it against the `Modules/` directory using `php-cs-fixer fix Modules/ --verbose`. Or run it individually for one module only, whichever you prefer.
+
+
+## Getting setup
+### Modules 
+
+- Have an installation of [AsgardCMS/Platform](https://github.com/AsgardCms/Platform) 
+- Remove `.git/` directory
+- Remove all modules from `composer.json` file
+- `cd` into the `Modules/` folder and clone each Module individually
+- Install AsgardCMS as usual `php artisan asgard:install`
+
+### Themes
+
+This is the same as modules except `cd`-ing into the `Themes/` folder and cloning desired themes in there.
+
+
+
+## Making changes
+
+Once you have your copy of AsgardCMS installed and configured for contributing purposes, you're ready to make changes.
+
+AsgardCMS follows a workflow similar to **[Git Flow branching model](https://www.atlassian.com/git/tutorials/comparing-workflows/gitflow-workflow/)**.
+
+This means:
+
+- For a new feature: 
+	- Create a branch `feature/your-new-feature-name`
+	- Add you changes
+	- Make sure the test suite for the module still passes
+	- [Squash commits](https://ariejan.net/2011/07/05/git-squash-your-latests-commits-into-one/) if necessary to create a nice history
+	- Send a pull request to the `develop` branch of the module/theme your modifying
+- For a hotfix:
+	- Create a branch `hotfix/your-hotfix-name`
+	- Add a failing test that reproduces the found bug
+	- Add you changes by making the test pass
+	- [Squash commits](https://ariejan.net/2011/07/05/git-squash-your-latests-commits-into-one/) if necessary to create 	a nice history
+	- Send a pull request to the `develop` branch of the module/theme your modifying
+
+
+# Additional Resources
+
+* [General GitHub documentation](http://help.github.com/)
+* [GitHub pull request documentation](http://help.github.com/send-pull-requests/)
+* `#asgardcms`IRC channel on freenode.org
+