Add example cover

src/components/presentational/covers/Default.js

@@ -0,0 +1,16 @@
+import React from 'react'
+
+export default ({ showAppHandler }) => (
+  <div className='default-cover-container'>
+    <h3>Here's an example cover.</h3>
+    <p>Replace it with a more descriptive one:</p>
+    <ul>
+      <li>Create a new component in <code>components/presentational/covers</code>.</li>
+      <li>Import in in <code>components/Dashboard.jsx</code> in the <code>render</code> function.</li>
+    </ul>
+    <br /><br />
+    <div>
+      <button onClick={showAppHandler}>Go to app</button>
+    </div>
+  </div>
+)