docs: set-up sapper template

docs/src/routes/blog/index.svelte

@@ -0,0 +1,34 @@
+<script context="module">
+  export function preload({ params, query }) {
+    return this.fetch(`blog.json`)
+      .then(r => r.json())
+      .then(posts => {
+        return { posts };
+      });
+  }
+</script>
+
+<script>
+  export let posts;
+</script>
+
+<style>
+  ul {
+    margin: 0 0 1em 0;
+    line-height: 1.5;
+  }
+</style>
+
+<svelte:head>
+  <title>Blog</title>
+</svelte:head>
+
+<h1>Recent posts</h1>
+
+<ul>
+  {#each posts as post}
+    <li>
+      <a rel="prefetch" href="blog/{post.slug}">{post.title}</a>
+    </li>
+  {/each}
+</ul>