add paper trail

app/controllers/admin/application_controller.rb

@@ -2,5 +2,12 @@
 module Admin
   class ApplicationController < Administrate::ApplicationController
     before_action :authenticate_admin_user!
+    before_action :set_paper_trail_whodunnit
+
+    # used by #set_paper_trail_whodunnit
+    def current_user
+      # add admin prefix to differentiate from a customer
+      "admin/#{current_admin_user.id}"
+    end
   end
 end