Add clarification around preset icons

data/presets/README.md

@@ -75,6 +75,13 @@ Each field definition lives in a separate file in `data/presets/fields`. The fie
 name (used in the preset `fields` property) is the name of the file (minus the `.json`
 extension).
 
+## Icons
+
+Preset icons in iD are pulled from the open source POI icon set, 
+[Maki](http://www.mapbox.com/maki/). Icons are stored in `dist/img/maki-sprite.png`.
+The icons are identified in iD by the same name as they are on the Maki home. Use those 
+names when identifying the icon to be used for a given preset. 
+
 ## Building
 
 To build presets, all you need to to is run `make`.