more interesting hello world (#1428)

Author: Rich-Harris

apps/svelte.dev/content/examples/00-introduction/00-hello-world/+assets/App.svelte

@@ -1,5 +1,11 @@
 <script>
-	let name = 'world';
+	let name = $state('world');
+	let count = $state(0);
 </script>
 
 <h1>Hello {name}!</h1>
+
+<input bind:value={name} />
+<button onclick={() => count += 1}>
+	clicks: {count}
+</button>