DOC: Make explicit in pandas IO doc the imports and options
- [x] works on #28038 
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [x] Removes code header from IO doc page.
- [x] Uses explicit imports in the IO doc page of user guide on first occurrence of requirement.

Reference @datapythonista - [149](https://github.com/python-sprints/pandas-mentoring/issues/149)