There's a new update to the way we're delivering the notifications now, so basically: no more waiting for the newest version of the game to support notifications.
To enable your Achievement Notifications, first make sure that you have claimed and installed the 16 Free DLC pack. You should now see a new Game Overlay setting in the client (enabled by default), use this toggle to enable or disable the feature.
If you don't see your notifications - make sure that the feature was enabled for you automatically, or simply try turning it off and on again.
Enjoy! :)
Post edited November 13, 2015 by Konrad