Add contributing documentation

Author: xterao

CONTRIBUTING.md

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+# Contributing to Doma Tools for IntelliJ
+
+Thank you for your interest in contributing to this project!
+
+Please follow the guidelines below to set up your environment and submit contributions.
+
+## License
+
+All original contributions to Doma Tools are licensed under ASL - [Apache License, version 2.0](https://www.apache.org/licenses/LICENSE-2.0) or later.
+
+## About This Project
+
+This plugin project is based on the [IntelliJ Platform Plugin Template](https://github.com/JetBrains/intellij-platform-plugin-template).
+
+For other basic project information and best practices, please refer to the template repository.
+
+## Reporting Issues
+
+- Use the [GitHub Issues page](https://github.com/domaframework/doma-tools-for-intellij/issues) to report bugs or request features.
+
+## Contact
+
+Let's work together to make this project better! 
+
+If you have any questions or suggestions, feel free to open an issue or contact the maintainers via GitHub.
+Write the issue in English to share it with many people.
+
+## Prerequisites
+
+- **JDK 17**
+- **Git** (Install Git and configure your GitHub access)
+
+## Recommended IntelliJ IDEA Plugins
+
+We recommend installing the following plugins in IntelliJ IDEA to improve your development experience:
+
+You can install these plugins from `File > Settings > Plugins` in IntelliJ IDEA.
+
+- **[Plugin DevKit](https://plugins.jetbrains.com/plugin/22851-plugin-devkit)**
+- **[PsiViewer](https://plugins.jetbrains.com/plugin/227-psiviewer)**
+- **[Spotless Gradle](https://plugins.jetbrains.com/plugin/18321-spotless-gradle)**
+
+## Setting Up the Development Environment
+
+1. **Clone the Repository**
+
+   ```sh
+   git clone https://github.com/domaframework/doma-tools-for-intellij.git
+   cd doma-tools-for-intellij
+   ```
+
+2. **Open the Project in IntelliJ IDEA**
+   - Select `Open` and choose the project root directory.
+   - IntelliJ will automatically import the Gradle project.
+
+3. **Generate Custom Language Java Files (Grammar-Kit)**
+   - Before building the project, generate the lexer and parser Java files using Grammar-Kit tasks:
+     ```sh
+     ./gradlew generateLexer
+     ./gradlew generateParser
+     ```
+   - If you make changes to `Sql.bnf` or `Sql.flex`, be sure to re-run the above tasks to regenerate the Java files.
+   - If you encounter build errors related to generated sources, try deleting the generated `gen` directory and re-running the Grammar-Kit tasks.
+
+4. **Build the Project**
+   - Use the Gradle tool window or run:
+     ```sh
+     ./gradlew build
+     ```
+   - To generate a plugin zip file for local installation, run:
+     ```sh
+     ./gradlew buildPlugin
+     ```
+     The zip file will be created in the `build/distributions` directory and can be installed locally in IntelliJ IDEA.
+
+5. **Run/Debug the Plugin**
+   - Use the Gradle task `runIde` to launch a sandboxed IntelliJ instance:
+     ```sh
+     ./gradlew runIde
+     ```
+## Code Style
+
+We use [Spotless](https://github.com/diffplug/spotless) and [google-java-format](https://github.com/google/google-java-format) for code formatting and style checking.
+
+- To check or apply formatting, run the following Gradle tasks:
+  ```sh
+  ./gradlew spotlessCheck   # Check code format
+  ./gradlew spotlessApply   # Apply code format
+  ```
+- Alternatively, formatting will also be applied automatically when you build the project:
+  ```sh
+  ./gradlew build
+  ```
+
+Please ensure your code is formatted with Spotless before submitting a pull request.
+
+## Branch Naming Rules
+
+When creating a working branch, please follow the naming rules below according to the type of change:
+
+- Bug fixes: `fix/`
+- Documentation changes: `document/`
+- CI-related changes: `ci/`
+- Dependency updates: `dependencies/` (Note: Version upgrades for dependencies are handled automatically by Renovate)
+- New features: `feature/`
+- Refactoring: `chore/`
+
+For example, a bug fix branch might be named `fix/typo-in-readme`, and a new feature branch might be `feature/add-user-authentication`.
+
+## Submitting a Pull Request
+
+1. Fork the repository and create your branch from `main`.
+2. Make your changes and ensure all tests pass:
+   ```sh
+   ./gradlew check
+   ```
+3. Submit a pull request with a clear description of your changes.