chore: add CONTRIBUTING.md (#30)

Signed-off-by: Henry Schreiner <[email protected]>

Author: henryiii

CONTRIBUTING.md

@@ -0,0 +1,42 @@
+# Contributing to pyproject-fmt-rust
+
+Thank you for your interest in contributing to pyproject-fmt-rust! There are
+many ways to contribute, and we appreciate all of them. As a reminder, all
+contributors are expected to follow our [Code of Conduct](CODE_OF_CONDUCT.md).
+
+## Development Setup
+
+### Building the Project
+
+To work on the project:
+
+1. Install Rust (preferably through [rustup](https://rustup.rs)).
+2. Clone the repository.
+3. Build the project and run the unit tests:
+   ```bash
+   cargo test
+   ```
+
+
+## License
+By contributing to pyproject-rust-format, you agree that your contributions
+will be licensed under the [MIT License](LICENSE).
+
+Thank you for your contributions! If you have any questions or need further
+assistance, feel free to reach out via GitHub issues.
+
+## Tips
+
+### Always recompiling PyO3
+
+If you find PyO3 constantly recompiling (such as if you are running
+rust-analyser in your IDE and cargo test in a terminal), the problem is that
+PyO3 has a `build.rs` that looks for Python, and it will recompile if it is run
+with a different PATH. To fix it, put the following in `.cargo/config.toml`:
+
+```toml
+[env]
+PYO3_PYTHON = "./.venv/bin/python"
+```
+And make sure you have a `.venv` folder with Python in it. This will ensure all
+runs use the same Python and don't reconfigure.