added contribution notes

CONTRIBUTING.md

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+# Contributing
+
+
+## Notes about branches
+
+This project follows the principles of the 
+[GitFlow branching model](http://jeffkreeftmeijer.com/2010/why-arent-you-using-git-flow/)
+as [proposed by Vincent Driessen](http://nvie.com/posts/a-successful-git-branching-model/). According to this model you 
+will find these branches at the GitHub project page:
+
+-   The [master branch](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/tree/master) contains the current stable 
+    releases. No development is directly taking place in that branch.
+
+-   The [develop branch](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/tree/develop) represents the current state of 
+    development. Changes from this branch are merged into 
+    [master](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/tree/master) when a new version is released.
+
+-   For more complex features you may also find different feature branches. These are derived from
+    [develop branch](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/tree/develop) and are merged back / removed as 
+    soon as the feature is ready for release.
+
+> **Notice:** If you like to provide changes to this project, you should always use the 
+> [develop branch](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/tree/develop) as basis for your customization. Feel
+> free to create separate feature branches for any custom feature you like to share. 
+
+
+## Create a pull request
+
+We love pull requests. Here's a quick guide.
+
+-   Fork this project into you GitHub profile.
+
+-   Clone the [develop branch](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/tree/develop) of the repository to your 
+    local disk:
+    ```
+    git clone -b develop [email protected]:your-username/OpenEstate-PHP-Wrapper-Joomla.git
+    ```
+
+-   Do your changes to the local repository and push the changes back into your fork at GitHub.
+
+-   [Submit a pull request](https://github.com/OpenEstate/OpenEstate-PHP-Wrapper-Joomla/compare/) with the changes from your fork.
+
+At this point you're waiting on us. We like to comment on pull requests as soon as possible. We may suggest some changes 
+or improvements or alternatives.
+
+Some things that will increase the chance that your pull request is accepted:
+
+-   Test your changes.
+-   Write a [good commit message](http://tbaggery.com/2008/04/19/a-note-about-git-commit-messages.html).