Document the :shallow_path option for scope

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -493,6 +493,25 @@ module ActionDispatch
         #    end
         #
         # Helpers such as +posts_path+ will now be +sekret_posts_path+
+        #
+        # [:shallow_path]
+        #
+        #   Prefixes nested shallow routes with the specified path.
+        #
+        #   scope :shallow_path => "sekret" do
+        #     resources :posts do
+        #       resources :comments, :shallow => true
+        #     end
+        #
+        #   The +comments+ resource here will have the following routes generated for it:
+        #
+        #     post_comments    GET    /sekret/posts/:post_id/comments(.:format)
+        #     post_comments    POST   /sekret/posts/:post_id/comments(.:format)
+        #     new_post_comment GET    /sekret/posts/:post_id/comments/new(.:format)
+        #     edit_comment     GET    /sekret/comments/:id/edit(.:format)
+        #     comment          GET    /sekret/comments/:id(.:format)
+        #     comment          PUT    /sekret/comments/:id(.:format)
+        #     comment          DELETE /sekret/comments/:id(.:format)
         def scope(*args)
           options = args.extract_options!
           options = options.dup