Mention mac os x installation tools on getting started guide

guides/source/getting_started.textile

@@ -87,7 +87,10 @@ To install Rails, use the +gem install+ command provided by RubyGems:
 # gem install rails
 </shell>
 
-TIP. If you're working on Windows, you can quickly install Ruby and Rails with "Rails Installer":http://railsinstaller.org.
+TIP. A number of tools exist to help you quickly install Ruby and Ruby
+on Rails on your system. Windows users can use "Rails
+Installer":http://railsinstaller.org, while Mac Os X users can use
+"Rails One Click":http://railsoneclick.com.
 
 To verify that you have everything installed correctly, you should be able to run the following: