AQT doc devices and getting started tutorial

[alfrisch]

This PR adds AQT documentation and contains a *.md describing how to retreive tokens and URLs of AQT devices and a Jupyter notebook on a simple getting started example which shows how to execute a basic quantum circuit via the AQT API.

[balopat]

This looks great, thank you! I added some comments.
Also, a couple more things:

1. we'll need to add the headers to book.yaml
2. and to readthedocs rtd_docs/index.rst.
3. I'd love to have Access and Authentication separated out into the Guides section that would explain the users where they can sign up and then point them to the tutorial. We'll have similar ones for Pasqal and Google as well. Basically some of the sentences from the top section of your Getting Started guide but with a little bit more explanation what they can expect - e.g. I managed to sign up with my Google account and requested a subscription (the interface was clear), but it is unclear when how I will get a token.

Edit: I just realized this was exactly the content of devices.md. I would rename devices.md to access.md and rename the title to Access and authentication.

I'm happy to add 1 and 2 if you're okay with me pushing to your branch.

[alfrisch]

I'm happy to add 1 and 2 if you're okay with me pushing to your branch.

sure, go ahead, you can push to my branch

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[alfrisch]

@googlebot I fixed it.

[alfrisch]

changes have been added

[balopat]

Thank you! I added a next steps section as well that points to the getting started guide.

[CirqBot]

Automerge cancelled: A required status check is not present.

Missing statuses: ['cla/google']

[balopat]

@googlebot please rescan