Those big footprints you're seeing are the result of some bigfoots, as the Valley of the Yetis DLC is now available for Far Cry 4 as promised. You can pick this up on Ubishop or Steam, and here's the rundown on what this adds to the shooter sequel:

You’re stranded on a treacherous mountain ridge. You have no shelter and no immediate way off the mountain. You locate a camp, but you’ll have to fight to keep it. A strange (and deadly) cult is intent on taking it back and you’ll need to guard it from waves of enemies. All you want to do is survive, but you start to realize something else might is lurking in the shadows of the Himalayan Mountains, something inhuman. Can you survive in the Valley of the Yetis?