Installed Docker on Mac but can't find the command
I'm unsure which instructions you followed to install via
docker-3.4.1 is a very old version, so you have worse issues at foot than your PATH not containing the docker binary.
I recommend undoing your installation via pip and installing Docker for Mac the correct way. I believe the current stable version for MacOS is 18.03.
First go and uninstall whatever you did with
pip uninstall docker
Then go here https://docs.docker.com/docker-for-mac/install/ and dowload docker and follow the instructions and install it.