[scikit-learn] Experience with black formatting in scikit-learn for astropy

[Olivier Grisel]

I agree with Guillaume's answers.

I think it was a net benefit, even though it might be a bit annoying
to get the tooling right for first time contributors. We can probably
improve this by making the error messages on the CI more directive on
how to fix formatting issues by given copy-pastable commands to
install and run black in your branch.

Otherwise, I really like just pressing shift-ctrl-i to fix the
formatting when editing code in VS Code.

-- 
Olivier