You need the core game to run Dying Light The Following as its an expansion. The hardware requirement is therefore the same as Dying Light, with an i5 a GTX 780 and 8 GB RAM allowing you to reach 60 FPS at 1080p
Dying Light: The Following is a feature-heavy, story-based expansion pack. Driveable all-terrain dirt buggies will feature in a newmap that is the same size as all previous Dying Light maps combined.