The announcement was made by Microsoft's Larry Hryb on his Major Nelson blog earlier today:
"Starting today, Xbox Live Gold Members who don't have an Xbox One yet can start building their library of Xbox One games directly from Xbox 360 by taking advantage of the Games With Gold program. You have always been able to do it this via the web and my monthly Games With Gold posts. But now, on your Xbox 360 console head to the special Games With Gold section from the link on the home page of the console and you can 'purchase' it there."
Since this has already been available from the Xbox web store for a while, this is a relatively minor change. However, it should prove to be slightly more convenient for those looking to get a head-start by nabbing some free games before pulling the trigger on an Xbox One purchase.
Source: Major Nelson