IBMQ_Santiago is the default backend listed on the getting-started.ipynb, Santiago is retired

[Eriken79]

I think it would be more straightforward to put an active backend in on the getting started notebook, or even use aer_simulator. If I can get assigned to this issue, I will put in a PR changing the new default for the file to IBMQ_Manila. This one is active and should work for the purposes of getting started. However, I'm not sure if we want to direct all the traffic from the getting started page to Manila so correct me if that's wrong.
I also believe there should be an IBMQ.save_account() call with your API key in the getting-started account. I put that in the pull request as well.

[nbronn]

Done!