Update release workflow

[mxmehl]

We're using GitHub actions to make a pypi release somewhat automatically, the guide needs to be updated.

oss-red-flag-checker/CONTRIBUTING.md

Lines 43 to 50 in fe20f47

	* Upgrade dependencies: `poetry update`
	* Bump version in `pyproject.toml`
	* Build package: `poetry build`
	* Optional: publish to `test.pypi.org` with `poetry publish -r test-pypi` and test the package: `pip install -i https://test.pypi.org/simple oss-red-flag-checker`
	* Publish to PyPI: `poetry publish` (you may have to set your credentials/API key first)
	* Create Git tag: `git tag -s vx.y.z` (use a minimal message)
	* Push to GitHub: `git push && git push --tags`
	* Make a release on GitHub