How do I add autoincrement?

Hello,

     I am attempting to learn Ruby on Rails. I'm using Instant Rails
2.0 on a Windows computer. I really want the id number to
autoincrement, but I am not sure how to do that. The script that's
generated after the scaffold is listed below. Any help is appreciated.

class CreateMenuitems < ActiveRecord::Migration
  def self.up
    create_table :menuitems do |t|
      t.integer :id
      t.string :category
      t.text :categoryinfo
      t.string :name
      t.string :price
      t.text :iteminfo

      t.timestamps
    end
  end
    insert into menuitems values(NULL);
  def self.down
    drop_table :menuitems
  end
end

Remove this line. Rails will add the id field for you.