To install just drag and drop "gamedata" folder into your Stalker Clear Sky folder and say yes to overwrite if you have already a gamedata folder.
If this is your first attemp at installing mods then you have to go to your game folder, open "fsgame.ltx" with notepad and change this line:
$game_data$ = false| true| $fs_root$| gamedata
$game_data$ = true| true| $fs_root$| gamedata
Now you're done, I hope you'll enjoy this decorative mod :)