DOC: Fixing EX01 - added examples

- [x] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).

Towards https://github.com/pandas-dev/pandas/issues/37875

If I'm not mistaken, the parameter `downcast` for the `bfill` method should be `None`, `False`, or `infer` (per #53103 after pandas v2.1.0). So I did not include an example`dict` for it. 

`DataFrame.pipe` had examples already. 
`DataFrame.iterrows`also had examples, but needed the word "Examples" to pass the test. 

Thanks @DeaMariaLeon  Thank you @mroeschke 