向Hartl的教程添加一个联系人表单

I'm learning Rails by following Hartl's tutorial and making my own adjustments to it. Now, I would like to extent it and add a contact form that sends an email message. Such is not included in the tutorial, but by the end of chapter 10 we're learned to use the mailer method and we've configured SendGrid on Heroku.I'm learning Rails by following Hartl's tutoria