helpers: Add helper to locally run xfce-build
Precondition for running this helper is having docker installed, but as that is a sine-qua-non if you want to locally run the same build as on GitLab CI I guess that's acceptable.
Precondition for running this helper is having docker installed, but as that is a sine-qua-non if you want to locally run the same build as on GitLab CI I guess that's acceptable.