Add a link to a CDN (stylesheet)

To link to a CDN, simply add a link tag in the head of 'index.html'. The example below inserts a font-awesome CDN link.

<!DOCTYPE html>
<html lang="en">
<head>
  <base href="<%= APP_BASE %>">
  <meta charset="utf-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <title><%= APP_TITLE %></title>
  <meta name="description" content="">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <!-- insert css from CDNs here -->
  <link rel="stylesheet" href="https://opensource.keycdn.com/fontawesome/4.7.0/font-awesome.min.css" integrity="sha384-dNpIIXE8U05kAbPhy3G1cz+yZmTzA6CY8Vg/u2L9xRnHjJiAK76m2BIEaSEV+/aU" crossorigin="anonymous">
  <!-- inject:css -->
  <!-- endinject -->
</head>
<body>
...