Add zsh completion

Zsh completion is awful. BUT we can use the bash completion script with

autoload bashcompinit
bashcompinit
source /path/to/your/bash_completion_file

see https://stackoverflow.com/questions/3249432/can-a-bash-tab-completion-script-be-used-in-zsh to have zsh completion for free from bashrc completion.

With the new command

dojo completion zsh --file <filename>

The file will contain be the bash_completion script.