Just unpack and drop the folder ModFistDamage in your mod folder located in your your Witcher 3 directory. 
Example, mine is in C:\Program Files (x86)\Steam\SteamApps\common\The Witcher 3. 

If you don't have a mod folder (but you should since you should be using ESGO with my mod) just create one. 
Most importantly, use script merger after the installation and prioritize my mod over ESGO.