when you say "downloaded app" it sounds like you mean "URL Shortcut to my HTML 5 page" which pretty much any smartphone can do.
so by making any website that follows the >> HTML5 standards << you have a mobile web app.
for example, click the link below which points to the Sencha Touch 2 carousel sample
http://dev.sencha.com/deploy/touch/examples/production/carousel/index.html
(Use your mouse like a finger to slide around the images etc.)
There isn't a way to add an "app button" link to your mobile site using a link because that would be too much power for a webpage to mess up people's device home screen simply by clicking a link.
The best you can do is educate your users on how they can add your "app" using the native iOS functionality...
First click this button on any webpage you navigate to
Then click Add to Home Screen button