Add example how to use this module (with docker stack)

[benedikt-haug]

I found examples like the nextcloud repo to be immensely useful when trying to get something to work.

So I thought I should be giving back an example that "just works" with docker stack.

Please feel free to merge/modify/scrap it however you wish.

Thank you!

[x86dev]

Thanks for your contribution! Better late than never, but I just was too busy having a look at most of the PRs here.