Updated Python SDK Tutorial

[Stephen Rosen]

Hi everyone,

We've just overhauled the Python SDK tutorial to better introduce new users to the GlobusApp construct, which makes a large number of use cases easier to handle.

We're going to continue to work on more doc improvements in the coming months, but this is the most significant single change for the Python docs we're making and we wanted to let people know about it!

You can see the new documentation in our new "Getting Started" section:
https://globus-sdk-python.readthedocs.io/en/stable/user_guide/getting_started/

Best regards,
-Stephen