Create CONTRIBUTING.md with development setup and lintrunner guidance (#107)

This PR adds a comprehensive CONTRIBUTING.md file to help contributors
get started with the ONNX IR project development.

## What's included

The new CONTRIBUTING.md provides:

- **Links to project guidelines**: Direct links to the [Coding
Style](https://github.com/onnx/ir-py/wiki/Coding-style) and [Design
Principles](https://github.com/onnx/ir-py/wiki/Design-Principles) wiki
pages
- **Development environment setup**: Step-by-step instructions for
setting up a local development environment including virtual environment
creation and dependency installation
- **Lintrunner configuration**: Detailed guidance on using lintrunner
for code quality checks, including:
  - Installation with `lintrunner init`
  - Running linters with `lintrunner`
  - Applying automatic fixes with `lintrunner -a`
  - Formatting code with `lintrunner f`
- **Testing instructions**: How to run tests using both nox and pytest
directly
- **Build instructions**: Using nox or build module to package the
project
- **Contribution workflow**: Guidelines for submitting pull requests and
following project conventions

## Example usage

Contributors can now easily get started:

```bash
# Clone and setup
git clone https://github.com/onnx/ir-py.git
cd ir-py
python -m venv venv && source venv/bin/activate
pip install -r requirements-dev.txt && pip install -e .

# Initialize and run linting
lintrunner init
lintrunner -a --output oneline

# Run tests
nox -s test
```

The guide follows the repository's existing documentation style and
provides clear, actionable instructions for new contributors.

Fixes #106.

<!-- START COPILOT CODING AGENT TIPS -->
---

💡 You can make Copilot smarter by setting up custom instructions,
customizing its development environment and configuring Model Context
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---------

Signed-off-by: Justin Chu <justinchuby@users.noreply.github.com>
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: justinchuby <11205048+justinchuby@users.noreply.github.com>
Co-authored-by: Justin Chu <justinchuby@users.noreply.github.com>

Author: Copilot

CONTRIBUTING.md

@@ -0,0 +1,173 @@
+# Contributing to ONNX IR
+
+Welcome to the ONNX IR project! We appreciate your interest in contributing.
+
+## Code Style and Design Principles
+
+Before contributing, please familiarize yourself with our development guidelines:
+
+- **[Coding Style](https://github.com/onnx/ir-py/wiki/Coding-style)**: Our coding conventions and style guidelines
+- **[Design Principles](https://github.com/onnx/ir-py/wiki/Design-Principles)**: The core principles guiding the design of ONNX IR
+
+## Development Environment Setup
+
+### Prerequisites
+
+- Python 3.9 or higher
+- Git
+
+### Setting up the Development Environment
+
+1. **Clone the repository**:
+   ```bash
+   git clone https://github.com/onnx/ir-py.git
+   cd ir-py
+   ```
+
+2. **Create a virtual environment** (recommended):
+   ```bash
+   python -m venv venv
+   source venv/bin/activate  # On Windows: venv\Scripts\activate
+   ```
+
+3. **Install development dependencies**:
+   ```bash
+   pip install -r requirements-dev.txt
+   ```
+
+4. **Install the package in development mode**:
+   ```bash
+   pip install -e .
+   ```
+
+## Code Quality and Linting
+
+We use [lintrunner](https://github.com/suo/lintrunner) for code quality checks. The project includes several linters:
+
+- **RUFF**: Python linter and code formatter
+- **MYPY**: Static type checker
+- **EDITORCONFIG-CHECKER**: EditorConfig compliance checker
+
+### Setting up lintrunner
+
+1. **Initialize lintrunner** (this installs the required linting tools):
+   ```bash
+   lintrunner init
+   ```
+
+2. **Run all linters**:
+   ```bash
+   lintrunner
+   ```
+
+3. **Apply automatic fixes** where possible:
+   ```bash
+   lintrunner -a --output oneline
+   ```
+
+4. **Format code only**:
+   ```bash
+   lintrunner f --output oneline
+   ```
+
+### Linting specific files
+
+You can lint specific files or directories:
+```bash
+lintrunner src/onnx_ir/
+lintrunner path/to/specific/file.py
+```
+
+## Testing
+
+The project uses [nox](https://nox.thea.codes/) for testing across different environments and [pytest](https://pytest.org/) as the test runner.
+
+### Running tests with nox
+
+```bash
+# Run all tests
+nox -s test
+
+# Run tests with specific Python version (if available)
+nox -s test --python 3.11
+
+# Run tests with ONNX weekly build
+nox -s test-onnx-weekly
+
+# Run tests with PyTorch nightly
+nox -s test-torch-nightly
+```
+
+### Running tests directly with pytest
+
+If you prefer to run tests directly:
+
+```bash
+# Run all tests
+pytest
+
+# Run tests with coverage
+pytest --cov=onnx_ir
+
+# Run specific test file
+pytest tests/test_specific.py
+
+# Run doctests
+pytest src --doctest-modules
+```
+
+## Submitting Contributions
+
+### Before submitting
+
+1. **Ensure your code passes all linting checks**:
+   ```bash
+   lintrunner
+   ```
+
+2. **Run the test suite**:
+   ```bash
+   pytest path/to/test.py
+   ```
+
+### Pull Request Guidelines
+
+1. **Fork the repository** and create a feature branch from `main`
+2. **Write clear, descriptive commit messages**
+3. **Add tests** for new functionality
+4. **Update documentation** if needed
+5. **Ensure all CI checks pass**
+6. **Request review** from maintainers
+
+### Pull Request Description
+
+Use clear and descriptive PR description:
+```
+[component] brief description of change
+
+More detailed explanation if needed, including:
+- What was changed
+- Why it was changed
+- Any breaking changes
+```
+
+## Development Workflow
+
+1. **Create an issue** or comment on an existing one to discuss your proposed changes
+2. **Fork the repository** and create a feature branch
+3. **Make your changes** following our coding style and design principles
+4. **Add or update tests** as appropriate
+5. **Run linting and tests** locally
+6. **Submit a pull request** with a clear description of your changes
+
+## Getting Help
+
+- **Issues**: Report bugs or request features via [GitHub Issues](https://github.com/onnx/ir-py/issues)
+- **Discussions**: For questions and discussions, use [GitHub Discussions](https://github.com/onnx/ir-py/discussions)
+- **Documentation**: Visit the [official documentation](https://onnx.ai/ir-py/)
+
+## License
+
+By contributing to ONNX IR, you agree that your contributions will be licensed under the [Apache License 2.0](LICENSE).
+
+Thank you for contributing to ONNX IR! 🎉