页面<head>标签中设置：<link rel="apple-touch-icon" rel="external nofollow" href="/custom_icon.png">
不同尺寸的话：
<link rel="apple-touch-icon" rel="external nofollow" href="touch-icon-iphone.png"><link rel="apple-touch-icon" sizes="76x76" rel="external nofollow" href="touch-icon-ipad.png"><link rel="apple-touch-icon" sizes="120x120" rel="external nofollow" href="touch-icon-iphone-retina.png"><link rel="apple-touch-icon" sizes="152x152" href="touch-icon-ipad-retina