DOC: improve description of the example which dataframe has two rows
improve description of the example which dataframe has two rows

- [ ] closes #36970
- [ ] tests added / passed
- [ ] passes `black pandas`
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @yonashub! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:



There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2020-10-11 18:32:15 UTC Thanks @yonashub 

In the future, it would be better to create a new branch when submitting PRs, see the contributing guide