better documentation about the progress function

README.md

@@ -57,7 +57,9 @@ If you need to manually query the progress of the user, use the progress method
 There is also a `progressFunction` option where you can provide a function that will be called each time the user erases a new area. It receives as argument the normalized progress value (0.0 to 1.0).
 
 	$('#yourImage').eraser( {
-		progressFunction: someInterfaceUpdatingFunction
+		progressFunction: function(p) {
+			console.log(Math.round(p * 100) + '%');
+		}
 	});