DOC: The argument of pandas.DataFrame.to_markdown is unfriendly
#### Location of the documentation

https://pandas.pydata.org/docs/dev/reference/api/pandas.DataFrame.to_markdown.html


#### Documentation problem

The document of `pandas.DataFrame.to_markdown` is unfriendly because many options are shown as `**kwargs`.
I think these arguments should be documented explicitly like a `to_csv`.

https://pandas.pydata.org/docs/dev/reference/api/pandas.DataFrame.to_csv.html


#### Suggested fix for documentation

All arguments supported by `to_markdown` should be shown at document.
If don't mind, I would like to tackle this improvement.