readme improvements

README.md

-# Leaflet.Marker.rotate
+# Leaflet Marker rotate
 
 This is a plugin for [Leaflet](http://leafletjs.com/). It allows Markers
 (map icons) to be rotated using a CSS transform. Rotation is set in degrees.
 
 It is based on comments by users coomsie and runanet on
 [Leaflet/issues/386](https://github.com/Leaflet/Leaflet/issues/386).
+
+Features include an `iconAngle` marker option, and a `setIconAngle()` marker method.
+
+## Usage
+
+To set a marker's initial rotation:
+
+    var myMarker = L.marker(lat, lon, {
+        icon: L.icon(iconOptions),
+        iconAngle: 90,              // Rotate 90 degrees clockwise.
+    });
+    
+To rotate an existing marker:
+
+    myMarker.setIconAngle(180);     // Rotate 180 degrees.
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