Add contributing guidelines

.editorconfig

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+# This file is for unifying the coding style for different editors and IDEs
+# editorconfig.org
+
+root = true
+
+[*.php]
+charset = utf-8
+end_of_line = lf
+insert_final_newline = true
+trim_trailing_whitespace = true
+indent_style = space
+indent_size = 4

CONTRIBUTING.md

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+# How to contribute
+
+:tada: First off, thanks for taking the time to contribute! :tada:
+
+Contributing should be as easy as possible for anyone but there are a few things to keep in mind.
+The following guidelines for contribution should be followed if you want to submit a pull request. 
+
+## Coding Style
+* Make use of provided .editorconfig file.
+* Make sure to have End of File new lines.
+* Use 4 spaces for indentation.
+* Make use of docblocks and comments.
+
+## How to prepare
+
+* You need a [GitHub account](https://github.com/signup/free)
+* Submit an [issue](https://github.com/anselmh/CONTRIBUTING.md/issues) if there isn't one for the same matter yet.
+	* Describe the issue and include steps to reproduce if it's a bug.
+	* Ensure to mention the earliest version that you know is affected.
+* If you are able and want to fix this, fork the repository on GitHub
+
+## Make Changes
+
+* In your forked repository, create a topic branch for your upcoming patch. (e.g. `feature--name`)
+	* Usually this is based on the master branch.
+	* Create a branch based on master; `git branch
+	fix/master/my_contribution master` then checkout the new branch with `git
+	checkout fix/master/my_contribution`.  Please avoid working directly on the `master` branch.
+* Make sure you stick to the coding style that is used already.
+* Make use of the `.editorconfig`-file if provided with the repository.
+* Make commits of logical units and describe them properly.
+* Check for unnecessary whitespace with `git diff --check` before committing.
+
+* If possible, submit tests to your patch / new feature so it can be tested easily.
+* Assure nothing is broken by running all the tests.
+
+## Submit Changes
+
+* Push your changes to a topic branch in your fork of the repository.
+* Open a pull request to the original repository and choose the right original branch you want to patch.
+	_Advanced users may install the `hub` gem and use the [`hub pull-request` command](https://hub.github.com/hub.1.html)._
+* If not done in commit messages (which you really should do) please reference and update your issue with the code changes. But _please do not close the issue yourself_.
+_Notice: You can [turn your previously filed issues into a pull-request here](http://issue2pr.herokuapp.com/)._
+
+# Additional Resources
+
+* [General GitHub documentation](http://help.github.com/)
+* [GitHub pull request documentation](https://help.github.com/articles/about-pull-requests/)