Add Scroll Effect to Demo

Demo was not actually scrolling because scrollY was not bound.

site/content/tutorial/16-special-elements/05-svelte-window-bindings/app-a/App.svelte

@@ -4,7 +4,7 @@
 	let y;
 </script>
 
-<svelte:window/>
+<svelte:window bind:scrollY={y}/>
 
 <a class="parallax-container" href="https://www.firewatchgame.com">
 	{#each layers as layer}
@@ -85,4 +85,4 @@
 		padding: 0;
 		background-color: rgb(253, 174, 51);
 	}
-</style>
+</style>