docs: add contributing guidelines

CONTRIBUTING.md

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+# How To Contribute
+
+The `main` branch is protected, and all changes must be made through pull requests.
+
+## Send a Pull Request
+
+### Commit Conventions
+
+We use [Conventional Commits](https://www.conventionalcommits.org/) for commit messages, which allows a changelog to be auto-generated based on the commits.  
+Please read the guide through if you aren't familiar with it already.  
+Note that `fix:` and `feat:` are for actual code changes (that might affect logic). For typo or document changes, use `docs:` or `chore:` instead:  
+`fix: typo` -> `docs: fix typo`
+
+### Making the Pull Request
+
+When sending a pull request, make sure your PR's title also follows the Commit Convention.  
+
+If your PR fixes or resolves existing issues, please make sure you mention them in the PR description.  
+
+It's ok to have multiple commits in a single PR; you don't need to rebase or force push for your changes as we will use Squash and Merge to squash the commits into one commit when merging.
+
+In general, please also make sure that there are no unrelated changes in a PR. For example, if your editor has made any changes to whitespace or formatting elsewhere in a file that you edited, please revert these so it is more obvious what your PR changes.   
+And please avoid including multiple unrelated features or fixes in a single PR. 
+If it is possible to separate them, it is better to have multiple PRs to review and merge separately. In general, a PR should do one thing only.
+
+## Use ESLint
+
+We use ESLint for both linting and formatting.
+
+## No Prettier
+
+Since ESLint is already configured to format the code, there is no need to duplicate the functionality with Prettier.   
+To format the code, you can run `pnpm lint-fix` or referring the ESLint section for IDE Setup.
+
+If you have Prettier installed in your editor, we recommend you disable it when working on the project to avoid conflict.
+
+## Package Manager
+
+We use [pnpm](https://pnpm.io/) as our package manager.