what is a actual user experience for web apps functionality "add to your home screen"?

Good day all. I'm researching this topic for a while and I'm a bit confused, the question is: is there a "standard" user experience for a web app that has to e saved into the user phone?

what I mean: web apps are becoming really popular, it's easier to develop them they are quite cross OS, they are quite light and so on, everything is beautiful. I'd like to undertstand how to engage more the user, so one point is to add the icon of the web app on the user phone. Seems to be a lot of confusion about this topic:

chrome chooses if it has to ask the user to save the icon (that's weird) if there is a manifest file and if there are some events from the user (the user must come to the web app a couple of times it seems). https://developers.google.com/web/updates/2015/03/increasing-engagement-with-app-install-banners-in-chrome-for-android

iOS, just put your icons in the meta, and if the user is smart enough to save the page as a bookmark, that icon will go in the home screen. https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html

Windows, well... no informations about this actually.

I can be totally wrong, and I can misunderstood everything (I strongly hope this). But a thing is clear... there isn't any standard for this user experience, am I right? is there something I can do in order to achieve this engagement (make the user save the link of a webapp into his own homescreen), I don't like to teach my users on how to save a bookmark, I lost most of them in the process of reading "what is a bookmark" I'd like a button (or a js function to cal) that simply ask the user "hey do you like this web app? nice, save it on your home, click here!" I bet you got the idea. do you have any reading about this, any suggestion? is it really like this??