Summary

After recognizing that the documentation about configuration with environment variables is not perfectly clear wrt. their capitalization, @nicornk invited me the create a pull request. Here it is. Most notably I tried to go through the whole file and clarify where I had the feeling things were not completely precise or comprehensive.

I tried to verify all changes by inspecting config.py. Please double check that I did not misunderstand anything there.

Happy to hear your comments.