title: Create-react-app service worker not functioning
body: <p>I am working on a React progressive web app built from create-react-app, and am attempting to register a service worker. </p>
  
  <p>However, after following the documentation on create-react-app which merely says to change serviceWorker.unregister() to serviceWorker.register(), doesn't register anything.</p>
  
  <p>Even from a fresh create-react-app project this still doesn't work.</p>
  
  <p>The documentation seems very lean for this topic, is there anything else I need to do to register the default service worker generated by create-react-app?</p>