Categorical fixups3

Minor doc updates as part of #8375

* docstring in in cut/qcut + docstring examples #8077 (comment)
* whatsnew: In the note change "levels" to "categories" and s/Schultz/Schulz/
can you put a space before the '#'. alternatively you can do these in separate ipython blocks (I personally like the 2nd style, but I do the '#' comments too....)