Add favicon

static/index.html

@@ -11,7 +11,7 @@ found in the LICENSE file.
   <meta name="viewport" content="width=device-width, initial-scale=1.0">
   <meta name="description" content="">
   <meta name="author" content="">
-  <link rel="shortcut icon" href="favicon.png">
+  <link rel="shortcut icon" href="static/assets/img/favicon.png">
 
   <title>Syncthing Usage Reports</title>
   <link href="static/bootstrap/css/bootstrap.min.css" rel="stylesheet">