DOC: the document for DataFrameGroupby.hist is identical to that of DataFrame.hist
Here's the document for DataFrameGroupby.hist:
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.core.groupby.DataFrameGroupBy.hist.html

and here's an almost identical document for DataFrame.hist:
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.hist.html

I don't understand why pandas has a DataFrameGroupby.hist when DataFrameGroupby.plot.hist already exists. But given its existence, the document and especially the example at the bottom of the page needs to be adjusted for DataFrameGroupby.hist.
