Facilitate project contributions

[bittremieux]

• [ ] Enforce a consistent code style using black.
• [ ] Provide a git pre-commit hook for automatic code formatting.
• [ ] Include contributing guidelines.
• [ ] Include a code of conduct.
• [ ] Use setuptools_scm to automatically get the package number.
• [ ] Set up GitHub Action for automatic package release.
• [ ] Set up GitHub Action for unit tests.
• [ ] Extract notebooks to a separate repository and reorganize code directories.
• [ ] Move the documentation to readthedocs.