1) Download Grid (this is an add-on and not the full mod)
2) Download this add-on (makes sence right)
3) Unpack it to World of Warcraft/Interface/Addons/Grid/
4) It will ask to replace the file, click yes to replace
Note: If you update Grid, u gotta replace the file again with this add-on
I take no credits of making this, i downloaded it here in another compilation and took that part out, only problem was that it didn't work (errors)
So i only take credit of fixing the code and editing it a bit to make it smoother.