You'd have to add some code at the start of the game that would query a web server (itch?) to find the latest version of the game, parse the response and compare the games internal version with it. if it didn't match, branch to a 'please update me' screen and, maybe, open the download page in their web browser.
Unless you've got a server running high scores or it's a multi-player game, it seems like mostly it'll just annoy the user.