(Disclaimer: I own this game on a different account.)

1. Download the latest GZDoom for Linux and extract it into whatever folder you please.
2. Download the Slooter and extract jotun.ipk3 into that folder.
3. Run ./gzdoom
4.  Slootily sloot all the slooty sloots like a slooty slooter should.
5. ???
6. Profit.

Be aware it might not save to where you're expecting. (~/.config/gzdoom or somewhere like it.)

I'd also like to add that you can play SLOOTER on Android as well, provided you have an app that can run GZDoom.