Adding a legend?

The examples on `deck.gl` don't have an integrated legend but I saw [this suggestion on Pydeck](https://github.com/visgl/deck.gl/issues/4850#issuecomment-1188226561) and wonder if something similar would work with `lonboard`? There isn't an equivalent argument of `description` in the layers but it does look like [there is a description card component in `deck.gl` Jupyter widget](https://github.com/visgl/deck.gl/blob/02d6813584aa10d108e8cb28b7cc84ee6d6a31a9/modules/jupyter-widget/src/lib/components/description-card.js#L5) though not sure how to call it through `lonboard`..