Updating README.dev.md: Section on publishing python packages

[f-hafner]

In the guide, we are updating the recommendations for publishing a python package on pypi with github actions: NLeSC/guide#323.

To be consistent, we should also update the corresponding instructions in the README.dev.md: the new recommended way is github actions, and the part on twine will be removed or mentioned for debugging.

What do you think? I could make a PR.