Add Contributing guide

CONTRIBUTING.md

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+# Contributing
+
+Thank you for having interest in contributing this project!
+
+## Bugs, Typo, and Refactoring
+
+Please create an issue or pull request.
+
+## Proposing a Change
+
+I recommend to create an issue. 
+
+## Docs
+
+I'm not familiar with English, so I especially thank you for documents' corrections.
+
+## Testing
+
+Please update the tests to reflect your code changes.
+
+Pull requests will not be accepted if they are failing on GitHub actions.
+
+## Release
+
+This package is published by using [changesets](https://github.com/changesets/changesets).
+
+Please add changeset file when you make PR.
+
+You can generate it by using the following command.
+
+```bash
+pnpm changeset
+```
+
+The maintainer will publish this package after merging your PR.