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CONTRIBUTING.md

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-Nog in te vullen.
+# Contributing
+
+We – [VNG realisatie](https://www.vngrealisatie.nl/) and the maintainers of this project – know we can only create this standard together with you. Thus we appreciate your input, enjoy feedback and welcome improvements to this project and are very open to collaboration.
+
+We love issues and pull requests from everyone.
+
+## Problems, suggestions and questions in Issues
+
+You don't need to change any of our code or documentation to be a contributor. Please help development by reporting problems, suggesting changes and asking questions. To do this, you can [create a GitHub Issue](https://help.github.com/articles/creating-an-issue/) for this project in the [GitHub Issues for VNG-Realisatie/gemma-zaken](https://github.com/VNG-Realisatie/gemma-zaken/issues).
+
+## Documentation and code in Pull Requests
+
+If you want to add to the documentation or code of one of our projects you should make a Pull Request. If you never used GitHub, get up to speed with [Understanding the GitHub Flow](https://guides.github.com/introduction/flow/).
+
+### 1. Make your changes
+
+This project uses the **OneFlow branching model** and workflow. When you've forked this repository, please make sure to create a feature branch following the OneFlow model. Read this [short blogpost](http://endoflineblog.com/oneflow-a-git-branching-model-and-workflow) when you're not yet familiar with OneFlow.
+
+Add your changes in commits [with a message that explains them](https://robots.thoughtbot.com/5-useful-tips-for-a-better-commit-message). Document choices or decisions you make in the commit message, this will enable everyone to be informed of your choices in the future.
+
+If you are adding code, make sure you've added and updated the relevant documentation and tests before you submit your pull request. Make sure to write tests that show the behaviour of the newly added or changed code.
+
+### 2. Pull Request
+
+When submitting the pull request, please accompany it with a description of the problem you are trying to address and the issue numbers that this Pull Request fixes/addresses.
+
+### 3. Improve
+
+All contributions have to be reviewed by someone.
+
+It could be that your contribution can be merged immediately by a maintainer. However, usually, a new Pull Request needs some improvements before it can be merged. Other contributors (or helper robots) might have feedback. If this is the case the reviewing maintainer will help you improve your documentation and code.
+
+If your documentation and code have passed human review and have passed the automated tests, it is merged.
+
+### 4. Celebrate
+
+Your ideas, documentation and code have become an integral part of this project. You are the Open Source hero we need.
+
+---
+
+For more information on how to use and contribute to this project, please read the [`README`](README.md).Nog in te vullen.