DOC: Fix docstring of read_csv and related methods
The next Excel related functions contain many errors as reported by `scripts/validate_docstrings.py`:
- pandas.read_table
- pandas.read_csv
- pandas.read_fwf

We should fix them, following our standards: https://pandas.pydata.org/pandas-docs/stable/contributing_docstring.html

The validation script should not report errors after they are fixed.

