01-basics/app-a/App.svelte: add structure of svelte file so it is clear to users reading the docs

site/content/tutorial/01-introduction/01-basics/app-a/App.svelte

@@ -1 +1,11 @@
-<h1>Hello world!</h1>
+<script>
+  let name = "Svelte";
+</script>
+
+<h1>Hello {name}</h1>
+
+<style>
+  h1 {
+    color: blue;
+  }
+</style>