Explain rationale behind Leaflet.Toolbar plugin.

README.md

@@ -2,3 +2,16 @@ Leaflet.Toolbar
 ===============
 
 Extensible, flexible toolbar class for Leaflet maps.
+
+Why Leaflet.Toolbar?
+---------------
+
+Leaflet.draw exports an `L.Toolbar` class, but one look at it is enough to tell that it wasn't designed to serve as a general-purpose constructor for Leaflet toolbars.  For example:
+* Icons for all toolbar actions are given CSS classes prefixed with `leaflet-draw`.  Plugin developers aren't able to customize the CSS classes associated with each action.
+
+What is a toolbar?
+---------------
+
+A toolbar is a UI element which exposes to users a set of actions.  Actions are triggered by clicks and may change the state of the map, add new layers to the map, or change the state of existing layers.
+
+