It's already supported for all web exports, assuming you have a secure (HTTPS) host.
Oh, I didn't explain right
Yes, we can install the game through browser menu, but I'm about to add some in-game button, or banner with a message that makes app install easier
Because not every user knows about this feature
And this is a big problem of the html5 games on mobile
Hard to return to the game, small screen because of browser menus
So, ingame button could be handy