add note about cookbook in helpers

README.rdoc

@@ -387,6 +387,12 @@ route handlers and templates:
     bar(params[:name])
   end
 
+=== Helper Cookbook Recipes
+
+There's a number of helper recipes in the {Sinatra
+Book}[http://sinatra-book.gittr.com/] as well as {community contributed
+recipes}[https://github.com/sinatra/sinatra-book-contrib/tree/master/helpers].
+
 === Using Sessions
 
 A session is used to keep state during requests. If activated, you have one