DOC: update contributing guidelines for black
Closes https://github.com/pandas-dev/pandas/issues/27226 
Starting this by copying some content from dask (https://github.com/dask/dask/pull/4983)

Also related to https://github.com/pandas-dev/pandas/issues/23616 (recommending pre-commit hooks)


ok lgtm. thanks @jorisvandenbossche 