shell completion scripts

[Eloquencere]

Hi, I use croc extensively in my workflow and as a result I have written my own simple zsh completion script, which works well me. Just thought of contributing it here so that, other people using the cli can also benefit from it.

It's just a zsh completion script since zsh has been my primary shell. It would be great if someone can guide me to include it in the file structure, I'm not really proficient in golang, I'm just happy with croc and would like to contribute to the project.