DOC: missing docstring substitution for Series/DataFrame.set_axis()
https://dev.pandas.io/docs/reference/api/pandas.Series.set_axis.html
https://dev.pandas.io/docs/reference/api/pandas.DataFrame.set_axis.html

![image](https://user-images.githubusercontent.com/13159005/72154883-b527de80-33a9-11ea-8593-91d2cc2a9aaf.png)
