initial readme update (#27)

Author: kylebarron

README.md

@@ -1,3 +1,7 @@
 # @geoarrow/deck.gl-layers
 
-[deck.gl](https://deck.gl) layers for rendering GeoArrow data.
+[deck.gl](https://deck.gl) layers for highly efficient rendering with [GeoArrow](https://geoarrow.org) data.
+
+![](assets/hero.jpg)
+
+<p style="text-align:center">3.2 million points rendered with a <code>GeoArrowScatterplotLayer</code>.</p>