If you followed the instructions to install the FloppyBird game you can skip the steps until making the gamefolder for snake.
Open Retroarch on your gameshell
Select Load Cores
Select Download Core
Connect your device to your gameshell with SSH
Lets move the core to the emulators folder.
(If you use another folder to save your downloaded cores navigate there)
mv ~/.config/retroarch/cores/chailove_libretro.so /home/cpi/apps/emulators
Make a folder for the game (start here if you allready have FloppyBird installed)
Navigate to the games folder
Download the Snake.chai file
Make the .sh file
(change Snake if you want another name in the menu)
retroarch -L /home/cpi/apps/emulators/chailove_libretro.so /home/cpi/games/Snake/Snake.chai
Save and quit
Move the icon to ~/apps/launcher/skin/default/Menu/GameShell
Make sure the icon has the same name as the .sh file. In this case Snake.png
Reboot and have fun
Watch out pressing the opposite direction of the way you are moving, it will kill the snake instant.