more additions to Usage instructions

README.rdoc

@@ -61,6 +61,8 @@ Specify actions you want logged in a controller
     end
 
 Make your models impressionable.  This allows you to attach impressions to an AR model instance.  
+Impressionist will automatically log the Model name (based on action_name) and the id (based on params[:id]), but in order to get the count of impressions (example: @widget.impression_count), 
+you will need to make your model impressionalble
 
     class Widget < ActiveRecord::Base
       is_impressionable