title: How to use Shopify api to update the cart "Note" from the "Additional content & scripts" box
body: <p>I need to add a Note after the user places their order and is sent to the confirmation page.  I know you can add code in the "Additional content &amp; scripts" and was wondering if anyone knew how to add an ajax call that would allow me to add a note to the order through there?</p>
  
  <p><strong>Something like</strong></p>
  
  <pre><code>&lt;script type="text/javascript"&gt;
      jQuery.post('/cart/update.js', {
        note: "NEW ORDER CUSTOM NOTE",
      });
    &lt;/script&gt;
  </code></pre>