The giveaway is live right now, so if you'd like to enter, feel free to head over to Jelly Deals and do so using their competition widget. There are multiple ways to enter and you can enter multiple times. If you don't fancy it, that's OK too, we can all continue on with our day regardless.
As it says over on the page itself, entry closes at 23:59:59 on Monday 23rd October and Humble Store gift keys will be emailed out to the winners on the game's launch day. Keep in mind that since you'll need an account for Blizzard Battle.net in order to redeem your key for the game.