Hello!

In https://github.com/python/cpython/blob/master/Lib/typing.py#L115-L117, there is a note about the io and re classes not being included in typing.__all__.  I am a relatively new user of typing, and I did `from typing import *` in my code.  I ran the code through mypy first, which reported no problems, but then running Python 3.6 failed with a NameError (name 'IO' is not defined).

Reading through the typing source, it's clear that this was an intentional decision.  So, instead of reporting a bug, I'd like to request a documentation enhancement!

The docs for typing make no mention of typing.io or typing.re.  So, my request is: In the sections for the IO/TextIO/BinaryIO and Pattern/Match classes, include text warning the user that these types are not imported when you do `from typing import *`.