add multiple class toggles example

This answers the immediate question I had when I first saw the `class:foo` syntax.

site/content/docs/02-template-syntax.md

@@ -600,6 +600,9 @@ A `class:` directive provides a shorter way of toggling a class on an element.
 
 <!-- Shorthand, for when name and value match -->
 <div class:active>...</div>
+
+<!-- Multiple class toggles can be included -->
+<div class:active class:inactive={!active} class:is-admin>...</div>
 ```