Add pre-commit flow

[mdeweerd]

I propose pre-commit.

pip install pre-commit
# Check spelling - you'll find several typos.
pre-commit run -a codespell 
# Format & check spelling - formatting keeps width limited (useful with raw text editor) and unifies formatting choices.
# Note: merge pull requests before reformatting README.md
pre-commit run -a
# Run on commit:
pre-commit install

[mikeroyal]

Thanks for doing this! I'll take a look at it and if everything looks good. I'll merge this in the next few days.

[mdeweerd]

Updated with a github action now.