feat: add contributing guide (#132)

CONTRIBUTING.md

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+# Contributing Guidelines
+
+_Pull requests, bug reports, and all other forms of contribution are welcomed!_
+
+This guide serves to set clear expectations for everyone involved with the project so that we can improve it together.
+
+## Writing Commit Messages
+
+Follow the [Conventional Commit style](https://www.conventionalcommits.org/en/v1.0.0/).
+
+## Submitting Pull Requests
+
+**Note: All contributions will be licensed under the project's license.**
+
+- **Smaller is better.** Submit **one** pull request per bug fix or feature. A pull request should contain isolated changes pertaining to a single bug fix or feature implementation. **Do not** refactor or reformat code that is unrelated to your change. It is better to **submit many small pull requests** rather than a single large one. Enormous pull requests will take enormous amounts of time to review, or may be rejected altogether.
+
+- **Coordinate bigger changes.** For large and non-trivial changes, open an issue to discuss a strategy with the maintainers. Otherwise, you risk doing a lot of work for nothing!
+
+- **Follow existing coding style and conventions.** Keep your code consistent with the style, formatting, and conventions in the rest of the code base. When possible, these will be enforced with a linter. Consistency makes it easier to review and modify in the future.
+
+- **Promptly address any CI failures**. If your pull request fails to build or pass tests, please push another commit to fix it.
+
+- **[Resolve any merge conflicts](https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/resolving-a-merge-conflict-on-github)** that occur.