~~Docker is not needed. You can run a subshell like ZSH directly in a shell from Bash in example. And you get set the executable path of each script like #!/usr/bin/env zsh. I don't get why a Docker is needed for this.~~
Edit: I should read more before commenting nonsense like this... It's already a topic in the article. My bad. I leave the comment here, so nobody else makes the same mistake.