Here it i…can’t sleep because of the heat 
STEP 1:
Make a new file in:
/home/cpi/apps/launcher/Menu/GameShell
and name that eg.:
Galaga.sh
then edit that file and put this command line in:
retroarch -L /home/cpi/.config/retroarch/cores/fb_alpha_libretro.so /home/cpi/games/MAME/galaga.zip
In my example I use the: fb_alpha_libretro.so core to play GALAGA…
GALAGA is located in the folder:
/home/cpi/games/MAME/galaga.zip
Hope this explanes the commandline so everybody can use it with there own favorite games
STEP 2:
make an icon for the launch menu and place that in :
/home/cpi/apps/launcher/skin/default/Menu/GameShell
Name it (in my example given) Galaga.png
Hope it works for everybody…