Update 10/29/18: Both 1.6 and 1.7 patches caused major problems with this mod. If you can't get it to work, check out some troubleshooting tips in the forums here.
KC:D's developer, Warhorse, went out of its way to try to make the game's combat adhere to medieval realism as much as possible, making combat quite a bit trickier than in your average fantasy RPG.
One of those concessions to realism is the lack of a reticle when preparing to fire an arrow, making accurate volleys nearly impossible -- sans blind luck or lots (and lots and lots) of practice.
If you'd prefer to add in standard game mechanics and pull out the realism element, this mod gives you a reticle for easier bow aiming.