Big Walk, the recently released multiplayer puzzle game from House House, has officially sold one million copies. It’s a major milestone to hit for any game, but it’s especially significant for an indie developer.  Big Walk’s publisher Panic shared the news with a post on social media earlier today, with an image you can see below. “In just six days, over one million of you have bought Big Walk, our co-op adventure all about talking and walking,” the post from…