Check kwargs description for all df and series plot submethods
After the Pandas Sprint we have had many changes, see in a week or so if they are consistent. See https://github.com/pandas-dev/pandas/pull/20155#discussion_r174304114

The description of this parameter for all `df/series.plot.*` methods should be
```
Additional keywords are documented in :meth:`pandas.Series.plot`
```

(respectively with `pandas.DataFrame.plot`)

Assign to myself.