The Add to Homescreen option is available through the Share menu in Safari on your iOS device. If you're not seeing the option, it's possible that you are viewing the app on an unsupported browser.
For example, if you clicked the link in an email you may be viewing it in Google or Gmail's web browser instead of in Safari. If so, it would look something like this:
Instead of like this:
Try copying the link, and then pasting into the address bar in Safari to see if that clears up the issue for you by following these instructions.