jQuery from Google’s CDN, with local fallback

<!-- Add JQuery from googles CDN -->
<script src="//ajax.googleapis.com/ajax/libs/jquery/1.9.1/jquery.min.js"></script>

<!-- If it doesn't load, load it locally -->
<script>window.jQuery || document.write('<script src="js/vendor/jquery-1.9.1.min.js"><\/script>')</script>

<!-- Then your custom JS -->
<script src="/js/main.js"></script>