Add wallpaper for grub

Signed-off-by: Peter Jung <admin@ptr1337.dev>

archiso/grub/grub.cfg

@@ -12,6 +12,9 @@ if loadfont "${prefix}/fonts/unicode.pf2" ; then
     set gfxmode="auto"
     terminal_input console
     terminal_output gfxterm
+    if [ -e "${cmdpath}/splash.png" ]; then
+        background_image "${cmdpath}/splash.png"
+    fi
 fi
 
 # Enable serial console