README: Fix import name in quickstart

[afitz0]

What was changed

In README.md correct a placeholder package name to the correct name used in the example.

Why?

So that copy-pasting the example runs correctly, without modifications.

Checklist

How was this tested:

• Installed python sdk.
• Ran quickstart example, making no additional modifications to the code.
• Witness Result: Hello, my name! as expected.

[CLAassistant]

All committers have signed the CLA.

[cretz]

I was expecting people to have their workflows somewhere else, but this makes sense for a quick start. Arguably it could be .run_worker. For best practices of course, you probably wouldn't put your workflow in the worker's main script.