Add manifest

index.html

@@ -5,6 +5,7 @@
   <meta charset="utf-8">
   <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
   <link rel="stylesheet" href="css/bootstrap.min.css">
+  <link rel="manifest" href="manifest.json">
   <title>Hello, world!</title>
 </head>