Create GeoJSON example notebook

[BibMartin]

Adresses #89 and centralize GeoJSON examples.

[ocefpaf]

A few points:

• Beautiful! We need to find a way to auto-generate docs from notebooks like this.
• It is hard to review the notebook on GitHub, so I am merging as-is and review it later.
• We all need to take a look at at to point people to this in issues. I am sure that notebook will answer most of the questions we will get once we release.

Thanks @BibMartin!