Sign In and Out page doesn't mention how to sign in with sites, which makes it unhelpful for Tableau Online users.

https://tableau.github.io/server-client-python/docs/sign-in-out 

By digging further into the Authentication API reference, you can learn how to sign in to Tableau Online. But at first look, it makes it seem like this library is only intending to support Tableau Server users.

We should add an example that shows signing into Tableau Online.

