add migration template

lib/generators/active_record/templates/migration.rb

@@ -0,0 +1,8 @@
+class TwoFactorAuthenticationAddTo<%= table_name.camelize %> < ActiveRecord::Migration
+  def self.change
+    change_table :<%= table_name %> do |t|
+      t.string   :second_factor_pass_code     , :limit => 32
+      t.integer  :second_factor_attempts_count, :default => 0
+    end
+  end
+end