DOC: more specific str.split() explanation
In the docs we see:
![screen shot 2019-03-05 at 14 17 32](https://user-images.githubusercontent.com/16627482/53811498-73403780-3f51-11e9-9591-8489096218b1.png)
but in fact the default behaviour of `str.split()` is more complicated than using `str.split(" ")` as detailed in the [python 3 documentation](https://docs.python.org/3/library/stdtypes.html#str.split). Perhaps linking to this explanation of the splitting algorithm would be preferable or writing something slightly more verbose would be preferable? Even saying "consecutive  whitespace" would probably be enough.
