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CONTRIBUTING.md

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+# Contributing to XcodeGen
+
+There are various ways to contribute to XcodeGen, and all are welcome and appreciated!
+
+- [Bug Reports](#bug-reports)
+- [Feature Requests](#feature-requests)
+- [Answering Questions](#answering-questions)
+- [Example Specs](#example-specs)
+- [Documentation](#documentation)
+- [Code](#code)
+
+## Bug reports
+Open issues about problems you may be encountering. When doing so please mention the version you're using `xcodegen --version`.
+
+## Feature Requests
+If you have a good idea for a feature or enhancement open an issue. 
+
+## Answering Questions
+Look through the open issues and answer any questions you can.
+
+## Example specs
+Submit your open source xcodegen spec to the [Examples](Docs/Examples.md) page.
+
+## Documentation
+Improve the documentation in the [Docs](Docs) directory.
+
+## Code
+You can submit your own code. This can be bug fixes or new features. If you're not sure what to work on check out the open [Issues](https://github.com/yonaskolb/XcodeGen/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-desc)
+
+### Getting started
+Make sure you have at least Xcode 9.2 installed.
+
+First clone the repo:
+```shell
+git clone https://github.com/yonaskolb/XcodeGen.git
+cd XcodeGen
+make
+```
+
+To make editing easier you can generate the Xcode project using Swift PM:
+
+```shell
+swift package generate-xcodeproj
+```
+
+### Targets
+- `ProjectSpec`: Project spec definitions, loading, parsing and validation
+- `XcodeGen`: XcodeGen CLI
+- `XcodeGenKit`: All the logic for generation
+- `XcodeGenKitTests`: Generation tests
+
+### Tests
+Before submitting your PR run the tests to make sure they pass. This can be done either in Xcode or by running `swift test`.
+
+As part of the tests there is a [TestProject](/Tests/Fixtures/TestProject) fixture that will be generated, and if the generated xcode project has any diff in it the test will fail. If the diff is a valid change, commit it as part of your changes.
+
+> Note that sometimes having the `TestProject` open in Xcode will generate it's own diffs, so make sure to have it closed when running the tests.
+
+If your change contains any new features or logic changes please add a unit test of your own to cover it. If it's a new feature, see if it can be integrated into the `TestProject` by adding any required files and then editing the [project spec](/Tests/Fixtures/TestProject/project.yml).