Add QA with Citations example to the Cookbook

[alonsosilvaallende]

As requested by @rlouf this PR adds a question answering with citations example to the Cookbook using llama-cpp-python.

[rlouf]

Awesome, thank you! Two things:

1- Can you add a link to this file here: https://github.com/outlines-dev/outlines/blob/main/mkdocs.yml so it shows in the docs
2- Could you run pre-commit locally?

[alonsosilvaallende]

Thank you @rlouf
I have done both requests.

[rlouf]

Thank you for adding the example!