Add comprehensive CONTRIBUTING.md for Python SDK (#40)

Cover contribution types, bug reporting, PR workflow, dev setup,
code style (black/ruff), and testing (pytest). Include alpha status note.

Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: George-iam

CONTRIBUTING.md

@@ -1,16 +1,69 @@
-# Contributing
+# Contributing to the AXME Python SDK
 
-Thank you for your interest in contributing.
+Thank you for your interest in contributing. Every bug fix, test, and
+improvement helps the entire AXME ecosystem.
 
-## Development Workflow
+AXME is in alpha -- breaking changes may occur. We especially welcome feedback
+on API ergonomics.
 
-1. Open an issue to discuss changes.
-2. Create a branch from main.
-3. Add tests for all behavioral changes.
-4. Ensure CI passes before opening a PR.
+## Ways to Contribute
 
-## Pull Request Requirements
+- Fix bugs and improve error messages
+- Add missing API methods
+- Improve type hints and docstrings
+- Add test coverage
 
-- Clear summary and rationale
-- Test coverage for new behavior
-- Backward compatibility notes where applicable
+## Reporting Bugs
+
+Open a GitHub Issue at <https://github.com/AxmeAI/axme-sdk-python/issues>.
+Include:
+
+- SDK version and Python version
+- Minimal code to reproduce the problem
+- Full traceback or error output
+
+## Proposing Changes
+
+1. Fork the repository.
+2. Create a branch from `main` (e.g., `fix/improve-error-message`).
+3. Make your changes.
+4. Run tests and linters (see below).
+5. Open a pull request against `main` with a clear description.
+
+## Development Setup
+
+```bash
+python -m venv .venv
+source .venv/bin/activate
+pip install -e ".[dev]"
+```
+
+## Code Style
+
+This project uses **black** for formatting and **ruff** for linting.
+
+```bash
+black .
+ruff check .
+```
+
+All code must include type hints. Public functions and classes must have
+docstrings.
+
+## Running Tests
+
+```bash
+pytest
+```
+
+Tests should pass before you open a PR. If you are adding a new feature or
+fixing a bug, add a test that covers the change.
+
+## Code of Conduct
+
+Be respectful and constructive. We value clear communication and good-faith
+collaboration.
+
+## Contact
+
+Questions or feedback: hello@axme.ai