Update contributing guidelines

Author: daniel-jones-dev

CHANGELOG.md

@@ -5,6 +5,11 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 
+## [Unreleased]
+### Changed
+* Update contributing guidelines, we can now accept Pull Requests.
+
+
 ## [0.4.0] - 2022-05-24
 ### Added
 * Add support for document translation.
@@ -34,6 +39,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 Initial version.
 
 
+[Unreleased]: https://github.com/DeepLcom/deepl-php/compare/v0.4.0...HEAD
 [0.4.0]: https://github.com/DeepLcom/deepl-php/compare/v0.3.0...v0.4.0
 [0.3.0]: https://github.com/DeepLcom/deepl-php/compare/v0.2.0...v0.3.0
 [0.2.0]: https://github.com/DeepLcom/deepl-php/compare/v0.1.1...v0.2.0

CONTRIBUTING.md

@@ -1,4 +1,37 @@
-# Contribution guidelines
+# Contributing guidelines
 
-We are currently unable to accept Pull Requests. If you would like to suggest changes, please open an 
-[issue](https://github.com/DeepLcom/deepl-php/issues) instead.
+* [Code of Conduct](#code-of-conduct)
+* [Issues](#issues)
+* [Pull Requests](#pull-requests)
+
+## Code of Conduct
+
+This project has a [Code of Conduct](CODE_OF_CONDUCT.md) to which all
+contributors must adhere when participating in the project. Instances of
+abusive, harassing, or otherwise unacceptable behavior may be reported by
+contacting [[email protected]](mailto:[email protected]) and/or a
+project maintainer.
+
+## Issues
+
+If you experience problems using the library, or would like to request a new
+feature, please open an [issue][issues].
+
+Please provide as much context as possible when you open an issue. The
+information you provide must be comprehensive enough for us to reproduce the
+issue.
+
+## Pull Requests
+
+You are welcome to contribute code and/or documentation in order to fix a bug or
+to implement a new feature. Before beginning work, you should create an issue
+describing the changes you plan to contribute, to avoid wasting or duplicating
+effort. We will then let you know whether we would accept the changes.
+
+Contributions must be licensed under the same license as the project:
+[MIT License](LICENSE).
+
+Currently automated testing is implemented internally at DeepL, however we plan
+to implement publicly visible testing soon.
+
+[issues]: https://www.github.com/DeepLcom/deepl-php/issues

README.md

@@ -292,8 +292,8 @@ feature, please open an [issue][issues].
 
 ## Development
 
-We are currently unable to accept Pull Requests. If you would like to suggest
-changes, please open an [issue][issues] instead.
+We welcome Pull Requests, please read the
+[contributing guidelines](CONTRIBUTING.md).
 
 ### Tests