DOC: Update Contributing Guide to Point to Pandas Docstring Guide
I've seen a few PRs here and there that come in with the good intention of updating docstrings but don't follow the pandas docstring guide. Part of the problem may be that we don't explicitly point to this in the contributing guide, referencing instead still the NumPy standard:

https://pandas.pydata.org/pandas-docs/stable/contributing.html#about-the-pandas-documentation

Could be a simply fix for someone to update that section and reference the pandas docstring guide

https://python-sprints.github.io/pandas/guide/pandas_docstring.html