move more stuff into site-kit

site/src/routes/migration/index.svelte

@@ -0,0 +1,22 @@
+<script context="module">
+	export async function preload() {
+		const sections = await this.fetch(`migration.json`).then(r => r.json());
+		return { sections };
+	}
+</script>
+
+<script>
+	import { Docs } from '@sveltejs/site-kit'
+
+	export let sections;
+</script>
+
+<svelte:head>
+	<title>Migration • Sapper</title>
+
+	<meta name="twitter:title" content="Sapper migration guides">
+	<meta name="twitter:description" content="The next small thing in web development">
+	<meta name="Description" content="The next small thing in web development">
+</svelte:head>
+
+<Docs {sections}/>