Improve documentation for adding & styling vector layers

[wendellwt]

Does ipyopenlayers support vector layers with points or markers? Does it support using a marker image in a vector layer as shown in the OpenLayers Icon Symbolizer example?

I didn't see any examples or source code that had (plain) vector layers.

Thank you.

[mfisher87]

GeoJSON is supported: https://ipyopenlayers.readthedocs.io/en/latest/api_reference/index.html#ipyopenlayers.openlayers.GeoJSON

But the documentation about how to style vector layers is anemic!