add favicon to index.html

Author: papjuli

index.html

@@ -3,6 +3,7 @@
     <title>Rubber band method</title>
     <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
     <link rel="stylesheet" href="style.css">
+    <link rel="shortcut icon" type="image/png" href="favicon.ico">
     <meta charset="UTF-8">
     <meta name="viewport" content="width=device-width, initial-scale=1">
     <link rel="preconnect" href="https://fonts.googleapis.com">