Include more performance benefit info in the README

[philwolstenholme]

See #27

The code examples might be too opinionated perhaps, but I think they might be useful to show the HTML only approach vs the more dynamic approach.

[nucliweb]

Btw, You may not need loadCSS…, by Filament Group.

Another approach, without dependencies will be:

<script>
  const media = window.matchMedia('(min-width: 1024px)')
  if (media.matches) {
    const desktopCSS = document.createElement('link');
    desktopCSS.rel = 'stylesheet';
    desktopCSS.href = '/css/desktop.css';
    document.getElementsByTagName('head')[0].appendChild(desktopCSS);
  }
</script>