[README] Report issues to https://gitlab.labs.nic.cz/knot/deckard/issues

[pspacek]

Please report all issues to official repo URL: https://gitlab.nic.cz/knot/deckard/issues

You can log-in with your existing Github account. Simply go to https://gitlab.nic.cz/users/sign_in and click to image with Github logo.

This Github repo is just mirror of the official repo located at https://gitlab.nic.cz/knot/deckard/ .

Thank you for understanding.