chore: add CONTRIBUTING

Author: ymgyt

CONTRIBUTING.md

@@ -0,0 +1,30 @@
+## Pull Requests
+
+If you have a new feature in mind, please discuss the feature in an issue to ensure that your
+contributions will be accepted.
+
+1. Fork the repo and create your branch from `main`.
+2. If you've added code that should be tested, add tests.
+3. If you've changed APIs, update the documentation.
+4. Ensure the test suite passes with `nix flake check`.
+
+## Commit Message
+
+Commit message should follow [conventional commit](https://www.conventionalcommits.org/en/v1.0.0/).  
+type is one of the following.
+
+| commit type | description                         |
+|-------------|-------------------------------------|
+| `feat`      | add a new feature                   |
+| `fix`       | bug fix                             |
+| `perf`      | performance improvement             |
+| `doc`       | documentation                       |
+| `ci`        | continuous Integration and delivery |
+| `refactor`  | refactoring                         |
+| `chore`     | catch all                           |
+
+## License
+
+By contributing to `clc`, you agree that your contributions will be dual-licensed under
+the terms of the [`LICENSE-MIT`](./LICENSE-MIT) and [`LICENSE-APACHE`](./LICENSE-APACHE) files in the
+root directory of this source tree.