Fix overview document and a type hint

[mlelarge]

Very nice work! Thanks!
Just started playing with it and got an error with the Hello World example in the documentation. This small modification fixed the issue for me.

Another remark: experimenting in a Jupyter notebook does not work because of a pb with asynchio, see https://pypi.org/project/nest-asyncio/
The solution proposed there worked for me:

import nest_asyncio
nest_asyncio.apply()

It would probably be nice to refer to it in the documentation.

I hope this helps.
Best,
Marc

[rlouf]

Thank you for contributing @mlelarge!