Create CONTRIBUTING.md

CONTRIBUTING.md

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+## How to contribute
+We'd love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.
+
+## Preparing a pull request for review
+Ensure your change is properly formatted by running:
+
+```gradle
+./gradlew spotlessApply
+```
+
+Then dump binary API of this library that is public in sense of Kotlin visibilities and ensures that the public binary API wasn't changed in a way that make this change binary incompatible. 
+
+```gradle
+./gradlew apiDump
+```
+
+Please correct any failures before requesting a review.
+
+## Code reviews
+All submissions, including submissions by project members, require review. We use GitHub pull requests for this purpose. Consult [GitHub Help](https://docs.github.com/en/github/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/about-pull-requests) for more information on using pull requests.