Highlight `__geo_interface__` support in Documentation

[kai-tub]

Is your feature request related to a problem? Please describe.
I was not really aware that folium supports to display objects with a __geo_interface__ protocol until today.
I am relatively new to working with geographic data, so maybe it is obvious for other people,
but I was surprised that it worked without any issues.

Describe the solution you'd like
A note in the documentation that the __geo_interface__ protocol is supported with folium.features.GeoJson, which allows for extensive interoperability with various other Python libraries.

Implementation
I am not sure where the best place would be to highlight this feature. Maybe as a note in Quickstart with example usage of GeoPandas? And a note in the GeoJson documentation?

It is an awesome feature, but I feel like it could be easily overlooked (at least from my point of view as a beginner).

PS: Thanks for maintaining this awesome project! 👍

[Conengmo]

I think the docstring of GeoJson might be a good place for this: https://github.com/python-visualization/folium/blob/master/folium/features.py#L314

Do you want to make a PR?

[kai-tub]

I would be happy to :)

[kai-tub]

Should we also add an example?
Like loading from shapely or geopandas?
These seem to be the most prominent __geo_interface__ libraries that could be frequently combined for analysis with folium. (Again from a perspective of a newcomer to this field)

[Conengmo]

We already have this example notebook, would this be similar to what you are proposing: https://nbviewer.jupyter.org/github/python-visualization/folium/blob/master/examples/Geopandas_and_geo_interface.ipynb

[kai-tub]

Oh, I missed that example.
Ok, then I will only update the docstring

[kai-tub]

As a side-note:
I think that these examples should be more prominently displayed.
I was always looking at the documentation page and not the GitHub Readme and I feel like a link at the end of the Quickstart section can be easily overlooked. Maybe we could add an extra section to the tables of content, where there are links to all current examples? Then new users could more easily find starting points for their problems?

Just my 2cts :)

[Conengmo]

that's also a good idea. It has bothered me for a while that the example notebooks are not well ordered and have sometimes cryptic names. But I don't want to change the names, because there may be incoming links to them. Linking to them from the documentation sounds like a good way around this. Again, if you want to help with a PR for this that would be welcome.

[kai-tub]

Sure. :)
I will open both PRs later today.

[Conengmo]

Merged in #1425