This will unlock through natural gameplay after completing any Bow Mission found around the map (they are indicated on your map by, you guessed it, bow icons). You can get this almost immediately upon starting the game, after unlocking free roam.
An early Bow Mission you'll likely complete is "A Elbereth Golthoniel" which is in the Black Road area. This particular mission requires you to kill all uruk archers, with bonus points available for getting 10 headshot kills. Complete this (or any other Bow Mission) and the achievement is yours!