If you look at the contents of the .app, you can edit main.scpt in AppleScript Editor, but it's really just doing two things, creating the VM if necessary:

docker-machine create -d virtualbox --virtualbox-memory 2048 default

and populating environment variables for docker:

eval $(docker-machine env default)

Passing --shell zsh to docker-machine env doesn't seem to change its output. Does zsh understand commands like the following?

export DOCKER_MACHINE_NAME="default"

Yep, `docker-machine env` should work fine in zsh (I am a daily zsh and docker-machine user).

I didn't use it, and ended up following the instructions here: https://docs.docker.com/installation/mac/#from-your-shell