Nodoc Rails command.

The API isn't ready yet, which means we haven't documented it.

People can't make their own commands, so there's no reason to show it
in generated documentation.

railties/lib/rails/command.rb

 require 'rails/commands/commands_tasks'
 
 module Rails
-  class Command
+  class Command #:nodoc:
     attr_reader :argv
 
     def initialize(argv = [])