docs: add CONTRIBUTING.md with development guidelines (#62)

Add contribution guidelines including:
- Development setup instructions
- Code style guidelines (ruff, mypy, pytest)
- Channel development guide
- PR guidelines
- Issue reporting template
- Bilingual (EN/CN) documentation

Co-authored-by: haosenwang1018 <haosenwang1018@users.noreply.github.com>

CONTRIBUTING.md

@@ -0,0 +1,107 @@
+# Contributing to Agent Reach
+
+Thank you for your interest in contributing to Agent Reach! This document provides guidelines and instructions for contributing.
+
+## Getting Started
+
+1. Fork the repository on GitHub
+2. Clone your fork locally
+3. Create a new branch for your contribution
+4. Make your changes
+5. Run tests and linting
+6. Submit a pull request
+
+## Development Setup
+
+```bash
+# Clone your fork
+git clone https://github.com/YOUR_USERNAME/Agent-Reach.git
+cd Agent-Reach
+
+# Install in development mode
+pip install -e ".[dev]"
+
+# Install pre-commit hooks (optional but recommended)
+pre-commit install
+```
+
+## Code Style
+
+We use the following tools to maintain code quality:
+
+- **ruff**: Linting and import sorting
+- **mypy**: Type checking
+- **pytest**: Testing
+
+Run all checks before submitting a PR:
+
+```bash
+# Linting
+ruff check agent_reach tests
+ruff format agent_reach tests
+
+# Type checking
+mypy agent_reach
+
+# Tests
+pytest
+```
+
+## Adding New Channels
+
+Agent Reach uses a unified channel interface. To add a new platform:
+
+1. Create a new file in `agent_reach/channels/`
+2. Implement the channel contract (see existing channels for examples)
+3. Add tests in `tests/test_channels.py`
+4. Update `agent_reach/doctor.py` to include the new channel
+5. Update documentation
+
+## Pull Request Guidelines
+
+- **Small, focused changes** are preferred over large refactors
+- Include tests for new functionality
+- Update documentation if needed
+- Follow existing code style
+- Reference any related issues
+
+## Reporting Issues
+
+When reporting bugs, please include:
+
+- Python version
+- Operating system
+- Steps to reproduce
+- Expected vs actual behavior
+- Any error messages
+
+## Questions?
+
+Feel free to open an issue for questions or join discussions.
+
+---
+
+感谢您对 Agent Reach 的贡献！本文档提供了贡献指南。
+
+## 快速开始
+
+1. 在 GitHub 上 fork 仓库
+2. 本地 clone 您的 fork
+3. 创建新分支
+4. 提交更改
+5. 运行测试和 lint
+6. 提交 pull request
+
+## 代码规范
+
+- 使用 **ruff** 进行代码检查
+- 使用 **mypy** 进行类型检查
+- 使用 **pytest** 运行测试
+
+## 添加新渠道
+
+1. 在 `agent_reach/channels/` 创建新文件
+2. 实现渠道接口
+3. 添加测试
+4. 更新 doctor 检测
+5. 更新文档