"! + Tab" Shortcut

I would like to add a line to the emmet shortcut where you hit “! + Tab” and you get:

    <!DOCTYPE html>
    <html lang="en">
    <head>
      <meta charset="UTF-8">
      <meta name="viewport" content="width=device-width, initial-scale=1.0">
      <meta http-equiv="X-UA-Compatible" content="ie=edge">
      <title>Document</title>
    </head>
    <body>

    </body>
    </html>

I would like to add a line to the default text above with the line:
<link rel="stylesheet" type="text/css" href="style.css" />

How can I do this within atom that way it’s already there and that’s one step I don’t have to add to the head?

You can’t do this in Atom (although you can use Atom to do it). Since you’re using emmet, you’ll do it the Emmet way with a snippets.json file in the folder named in the Extensions path setting in the emmet package settings (it’ll be a folder called emmet/ in your user folder by default, but you can make it whatever you want).