Added additional documentation to prop_copy()

lib/class.js

@@ -56,6 +56,9 @@ var Class = function()
 /**
  * Copies properties to the destination object
  *
+ * If the method already exists, it will be overridden and accessible via either
+ * the parent prototype or by invoking this.__super().
+ *
  * The destination object is directly modified.
  *
  * @param  {Object}  props  properties to copy