documentation/db/migrate/20161003142332_add_confirmable_to_users.rb

class AddConfirmableToUsers < ActiveRecord::Migration[5.0]
  def change
    add_column :users, :confirmation_token, :string
    add_column :users, :confirmed_at, :datetime
    add_column :users, :confirmation_sent_at, :datetime
    add_column :users, :unconfirmed_email, :string
    add_index :users, :confirmation_token, unique: true
  end
end