Docs: hide toc until alpine has loaded

From https://alpinejs.dev/directives/cloak :

> Sometimes, when you're using AlpineJS for a part of your template, there is a
> "blip" where you might see your uninitialized template after the page loads,
> but before Alpine loads.
>
> `x-cloak` addresses this scenario by hiding the element it's attached to until
> Alpine is fully loaded on the page.
>
> For `x-cloak` to work however, you must add the following CSS to the page.
>
> ```
> [x-cloak] { display: none !important; }
> ```

Author: panglesd

asset/css/doc.css

@@ -1,3 +1,5 @@
+[x-cloak] { display: none !important; }
+
 div.odoc {
   max-width: 56rem /* 896px */;
   position: relative;