Adding Python 3 static type annotations ?

[pvergain]

Hi Vitor,

Thank you for your amazing Django tutorial !
I think it could be nice to add Python3 static type annotation to the code. The zulip (https://github.com/zulip/zulip) code has been 100% annotated and it helps a lot in reading and documenting the code.

See http://blog.zulip.org/2016/10/13/static-types-in-python-oh-mypy/

Thank you !