Fix issue #5803: Document repo-specific prompt customization

docs/modules/usage/prompting/repo-specific-customization.md

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+# Repository-Specific Prompt Customization
+
+OpenHands provides two powerful ways to customize its behavior for specific repositories:
+
+1. `.openhands_instructions` file for repository-wide guidelines
+2. `.openhands` directory for custom micro-agents
+
+## The `.openhands_instructions` File
+
+The `.openhands_instructions` file is a simple text file placed in the root directory of your repository that provides repository-specific context and guidelines to OpenHands. This file's contents are automatically injected into the prompt when OpenHands processes issues or pull requests.
+
+### What to Include
+
+Your `.openhands_instructions` file can contain information like the following:
+
+1. **Repository Overview**: A brief description of your project's purpose and architecture
+2. **Directory Structure**: Key directories and their purposes
+3. **Development Guidelines**: Project-specific coding standards and practices
+4. **Testing Requirements**: How to run tests and what types of tests are required
+5. **Setup Instructions**: Steps needed to build and run the project
+
+### Example `.openhands_instructions` File
+
+Your `.openhands_instructions` file can contain information like the following:
+
+```
+This repository is a Python package that provides utilities for data processing.
+
+Key directories:
+- src/data_utils/: Core data processing modules
+- tests/: Test files organized by module
+- docs/: API documentation and usage guides
+
+Development setup:
+1. Create a virtual environment: python -m venv venv
+2. Activate: source venv/bin/activate (Linux/Mac) or venv\Scripts\activate (Windows)
+3. Install dev dependencies: pip install -e ".[dev]"
+
+Code guidelines:
+- Follow PEP 8 style guide
+- All new code must have type hints
+- Maintain 90% test coverage for new features
+- Document public APIs using Google docstring format
+
+Testing:
+- Run tests: pytest tests/
+- Run type checks: mypy src/
+- Run linting: flake8 src/
+
+Common gotchas:
+- The data_loader module requires pandas>=2.0
+- Test data files must be placed in tests/fixtures/
+- Large data operations should use chunked processing
+```
+
+### Best Practices
+
+1. **Keep Instructions Updated**: Regularly update the file as your project evolves
+2. **Be Specific**: Include specific paths, patterns, and requirements unique to your project
+3. **Document Dependencies**: List all tools and dependencies required for development
+4. **Include Examples**: Provide examples of good code patterns from your project
+5. **Specify Conventions**: Document naming conventions, file organization, and code style preferences
+
+## The `.openhands` Directory
+
+The `.openhands` directory allows you to create repository-specific micro-agents that extend OpenHands' capabilities for your project. For detailed information about creating and using micro-agents, please refer to the [Micro-Agents documentation](../micro-agents.md).
+
+## Using Both Features Together
+
+The `.openhands_instructions` file and `.openhands` directory complement each other:
+
+- Use `.openhands_instructions` for repository-wide guidelines and context
+- Use `.openhands` directory for specialized, task-specific agents
+
+For example:
+1. `.openhands_instructions` defines your project's overall structure and standards
+2. Custom micro-agents in `.openhands` handle specific tasks like testing, deployment, or domain-specific operations
+
+This combination allows OpenHands to:
+- Understand your project's context and requirements (via `.openhands_instructions`)
+- Handle specialized tasks effectively (via custom micro-agents)
+- Maintain consistency with your project's standards
+- Automate repository-specific workflows