app: Create basic app.

app/src/pages/page-2.js

@@ -0,0 +1,16 @@
+import React from "react"
+import { Link } from "gatsby"
+
+import Layout from "../components/layout"
+import SEO from "../components/seo"
+
+const SecondPage = () => (
+  <Layout>
+    <SEO title="Page two" />
+    <h1>Hi from the second page</h1>
+    <p>Welcome to page 2</p>
+    <Link to="/">Go back to the homepage</Link>
+  </Layout>
+)
+
+export default SecondPage