pull me request

leave your comments and changes :)
Another way of storing data like this is as a method, like so:

```ruby
class Book
  def books
    [
      'Potter1',
      'Potter2',
      'Potter3',
      'Potter4',
      'Potter5',
    ]
  end
end
```

The effect is just the same, but a lot of people prefer using methods to constants.