默认添加网站到主屏幕，显示的图标为网站的截图
使用下面的标签可以自定义图标
<link rel="apple-touch-icon-precomposed" rel="external nofollow" href="icon.png">
该标签还支持size属性，可以指定不同尺寸
<link rel="apple-touch-icon-precomposed" sizes="57x57" rel="external nofollow" href="icon-57.png"><link rel="apple-touch-icon-precomposed" sizes="72x72" rel="external nofollow" href="icon-72.png"><link rel="apple-touch-icon-precomposed" sizes="114x114" rel="external nofollow" href="icon-114.png"><link rel="apple-touch-icon-precomposed" sizes="144x144" rel="external nofollow" href="icon-144.png">
另外apple-touch-icon也可以达到效果。区别看单词意思，一个有IOS默认图标高亮一个无。
参考：
https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html#//apple_ref/doc/uid/TP40002051-CH3-SW4