Generating consolidated rdocs like api.rubyonrails.com

How do I generate a consolidated set of rdocs for my local rails
installation like the docs at api.rubyonrails.com? Currently I have the
rdocs for each package ( actionpack, activerecord, etc… ) that were
autogenerated when I downloaded the gems. Is the api.rubyonrails site
doing something special or is there a rake task that will generate my
local docs the same way?

Thanks!