Add notebooks to documentation

[SarahAlidoost]

closes #100

This PR adds notebooks, and recipes to doc. It also reorganizes the doc. Preview the documentation here.

[sverhoeven]

All notebooks work except one, see inline suggestion.

The collapsed recipes at https://springtime--105.org.readthedocs.build/en/105/recipes/ look nice.

Why are we rendering the datasets notebooks, but downloading the example use case notebooks? Why not render them both? As you can add download link to rendered notebooks with https://github.com/danielfrg/mkdocs-jupyter#download-notebook-link

[Peter9192]

Nice work, the package already looks so much richer now 🤩
But it also highlights a few other this that would be nice to address (probably in follow-up items):

• Some R calls are very noisy. In rnpn we used --no-echo and captured stderr, we could consider doing this for all notebooks, perhaps as part of Standardize interface across data sources #92
• It would be nice to add some explanation about the various datasets and their sources.

[SarahAlidoost]

All notebooks work except one, see inline suggestion.

The collapsed recipes at https://springtime--105.org.readthedocs.build/en/105/recipes/ look nice.

Why are we rendering the datasets notebooks, but downloading the example use case notebooks? Why not render them both? As you can add download link to rendered notebooks with https://github.com/danielfrg/mkdocs-jupyter#download-notebook-link

Download links are added, see an example.

[SarahAlidoost]

• It would be nice to add some explanation about the various datasets and their sources.

@Peter9192 each notebook has a link to the data source. See an example. Are more explanations about datasets needed?