Update index.html

static/admin/index.html

@@ -4,6 +4,7 @@
   <meta charset="utf-8"/>
   <meta name="viewport" content="width=device-width, initial-scale=1.0"/>
   <title>Content Manager</title>
+  <script src="https://identity.netlify.com/v1/netlify-identity-widget.js"></script>
 </head>
 <body>
 <!-- Include the script that builds the page and powers Netlify CMS -->