代码：
<link rel="apple-touch-startup-image" href="milanoo_startup.png" />
横屏和竖屏：
<link rel="apple-touch-startup-image" media="screen and (orientation: portrait)" href="milanoo_startup.png" /> <!--竖-->
<link rel="apple-touch-startup-image" media="screen and (orientation: landscape)" href="milanoo_startup1.png" /> <!--横-->
iphone：320*460
ipad：
startup_portrait.png 768x1004
startup_landscape.png 748x1024