This worked with the AppImages that aferrero used to create in the past, but no longer works with the AppImages, maintained by @Lawrence37, that are auto created right now.
There used to be a wrapper script that was called when starting the image, at the moment rawtherapee is hard linked and there is no option to point to rawtherapee-cli.
As mentioned by @paperdigits, you can easily extract modern AppImages and then run it from there if you need to.
To extract:
cd /PATH/TO/RawTherapee.AppImage
./RawTherapee.AppImage --appimage-extract
You can now access rawtherapee-cli by its full path:
/PATH/TO/squashfs-root/usr/bin/rawtherapee-cli <cli_options_go_here>