The new default is 'both' to add "GNU Image Manipulation Program" as well as "gimp-2.8" to the menu.
See "pod2man --utf8 contrib/i3-dmenu-desktop | man /dev/stdin" for documentation. Use a line like this in your i3 config file: bindsym Mod1+p exec --no-startup-id ~/i3/contrib/i3-dmenu-desktop