It's working like before:
Go into the installationfolder\bin and open an command prompt. Here you'll find the file openfire-service.exe
Juste execute openfire-service.exe /install and you're done. Now you may wanna start it with openfire-service.exe /start.
But be careful: As a service it will not communicate directly with you. So if you've errors in your configuration, you'll get a service which shutdown itself immediately.