Add ZSH completion script

[bheisig]

Expected behavior

Support auto-completion for ZSH (Z Shell)

See issue #9 for details

Actual behavior

There is no script available for ZSH's auto-completion.

Steps to reproduce the behavior

idoitcli <tab><tab>
idoitcli re<tab>

Environment

Question	Answer
idoitcli version	0.5