Add comprehensive documentation for fx-test repo

docs/contributing.md

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+# 🤝 Contributing Guidelines
+
+We welcome contributions! Please follow these steps:
+
+1. **Fork** the repository.
+2. Create a feature branch: `git checkout -b feature/awesome-feature`.
+3. Implement your change locally and run `./fluxer/scripts/run_dev.sh` to ensure the stack builds.
+4. Run the CI tests: `./fluxer/scripts/ci/workflows/ci.py`.
+5. Commit with a clear message: `git commit -m "Add feature: …"`.
+6. Push and open a pull request.
+
+Adhere to the existing code style. All patches should include relevant tests.