Rails5新機能: テーブル・カラムへのコメント ref: http://qiita.com/akm/items/b6b59dc3641daf282a7b

file0.txt

# coding: utf-8
class DeviseCreateUsers < ActiveRecord::Migration[5.0]
  def change
    create_table :users, comment: 'ユーザ' do |t|
      ## Database authenticatable
      t.string :email,              null: false, default: "", comment: 'メールアドレス'
      t.string :encrypted_password, null: false, default: "", comment: '暗号化済みパスワード'
      (snip)
    end
  end
end

file1.txt

$ bin/rails db:migrate

file2.txt

ActiveRecord::Schema.define(version: 20160721083716) do
  create_table "users", force: :cascade, options: "ENGINE=InnoDB DEFAULT CHARSET=utf8", comment: "ユーザ" do |t|
    t.string   "email",                  default: "", null: false, comment: "メールアドレス"
    t.string   "encrypted_password",     default: "", null: false, comment: "暗号化済みパスワード"
    (snip)
  end
end