Add some rack links

railties/guides/source/rails_on_rack.textile

@@ -229,6 +229,8 @@ h3. Rails Metal Applications
 
 Rails Metal applications are minimal Rack applications specially designed for integrating with a typical Rails application. As Rails Metal Applications skip all of the Action Controller stack, serving a request has no overhead from the Rails framework itself. This is especially useful for infrequent cases where the performance of the full stack Rails framework is an issue.
 
+Ryan Bates' railscast on the "Rails Metal":http://railscasts.com/episodes/150-rails-metal provides a nice walkthrough generating and using Rails Metal.
+
 h4. Generating a Metal Application
 
 Rails provides a generator called +metal+ for creating a new Metal application:
@@ -286,6 +288,19 @@ Each string in the array should be the name of your metal class. If you do this
 
 WARNING: Metal applications cannot return the HTTP Status +404+ to a client, as it is used for continuing the Metal chain execution. Please use normal Rails controllers or a custom middleware if returning +404+ is a requirement.
 
+h3. Resources
+
+h4. Learning Rack
+
+* "Official Rack Website":http://rack.github.com
+* "Introducing Rack":http://chneukirchen.org/blog/archive/2007/02/introducing-rack.html
+* "Ruby on Rack #1 - Hello Rack!":http://m.onkey.org/2008/11/17/ruby-on-rack-1
+* "Ruby on Rack #2 - The Builder":http://m.onkey.org/2008/11/18/ruby-on-rack-2-rack-builder
+
+h4. Understanding Middlewares
+
+* "Railscast on Rack Middlewares":http://railscasts.com/episodes/151-rack-middleware
+
 h3. Changelog
 
 "Lighthouse ticket":http://rails.lighthouseapp.com/projects/16213-rails-guides/tickets/58