ios: add apple-touch-icon icon

Ref: https://webhint.io/docs/user-guide/hints/hint-apple-touch-icons/

index.html

@@ -6,6 +6,7 @@
     <meta name="viewport" content="width=device-width, initial-scale=1.0">
     <!--#include virtual="base.html" -->
 
+    <link rel="apple-touch-icon" href="images/apple-touch-icon.png">
     <link rel="stylesheet" href="css/all.css">
 
     <script>