Add development requirements

[HLasse]

It would be useful to add development requirements (e.g. a linter) for new contributors. For instance, I tried running black on the codebase which led to quite some changes, but you might be using a different linter [EDIT: seems from your CI that you're using flake8]. Specifying this in the requirements or CONTRIBUTING.rst would be helpful. (openjournals/joss-reviews#6154)

[misken]

Thanks, will do. I use PyCharm and its built in linter when writing code but, yes, the CI workflow uses flake8. As the CI part is new to me, I'll admit that I'm not clear on whether I should force PyCharm to use flake8. Suggestions?

[HLasse]

I would suggest forcing pycharm to use flake8 and adding flake8 as an optional dev requirement + adding a line in CONTRIBUTING that you use flake8 for linting