Rename Apple touch icon & add <link> to index.html

Ref h5bp/html5boilerplate.com@71b10e1
    h5bp/html5-boilerplate#1615
    https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html

src/index.html

@@ -5,6 +5,7 @@
         <title>Mobile Boilerplate: A best practice baseline for your mobile web app</title>
         <meta name="description" content="Mobile Boilerplate is a professional front-end template that helps you build fast and robust mobile web applications. Spend more time developing and less time reinventing the wheel.">
         <meta name="viewport" content="width=device-width, initial-scale=1">
+        <link rel="apple-touch-icon" href="apple-touch-icon.png">
         <link rel="stylesheet" href="//fonts.googleapis.com/css?family=Open+Sans:400,700">
 
         <!-- build:css css/main.css -->