Add additional pre-commit checks

[noahp]

This updates the pre-commit config with several additional checks, including:

• black (for python formatting)
• isort (for ordering python imports)
• several miscellaneous text-file checkers

Summary of changes:

• add the config and associated config files for the hooks
• update the checkers with pre-commit autoupdate
• update the README.md with information about pre-commit
• run pre-commit --all-files and commit/fix any violations

This does not enable pre-commit in CI; normally would be useful but might be kind of overkill/nuisance for this project.

[ChrisJefferson]

I'm happy with this, but it conflicts now (sorry)

[noahp]

Thanks @ChrisJefferson ! I ended up removing the CI check, didn't think it was really that helpful in practice