Add missing notebooks to the navigation

[sequoiap]

There are a few notebooks in the nbs/ folder that:

1. are useful (especially the probes example),
2. are built during docs generation, and therefore show up in search feature, but:
3. are not in the docs navigation bar

This pull request simply adds them. I assume they are complete and not adding them was simply an oversight?

[flaport]

Thanks @sequoiap