As news doesn't seem to have spread here from the General forum;

The beta for the PS4 can be found (and thus added to your PS4's PSN account) via the web based playstation store. It's hiding under 'Games' -> 'New Releases' (the one at the top next to the Playstation Plus option) -> 'New this week'. Should be the third item at the moment.

Once you've 'bought' the free item there, go to your PS4 and navigate to your library and tell it to start downloading. Hey presto you'll be ready for the beta.