ActionMailer - 如何添加附件？

attachments['document.pdf'] = File.read('/path/to/document.pdf')

attachments.inline['logo.png'] = File.read('/path/to/logo.png')

def welcome_email(user)
  @user = user
  attachments['document.pdf'] = File.read('/path/to/document.pdf')
  attachments.inline['logo.png'] = File.read('/path/to/logo.png')
  mail(to: @user.email, subject: 'Welcome to My App')
end

<%= attachments['document.pdf'].url %>
<%= attachments.inline['logo.png'].url %>