Setup initial CI

Summary

CI should include

• code linting (pylint is available at centrally supported CERN cc7 docker images)
• automated documentation build
• documentation publishing on the gem website
  • shall it be public? I guess so

Relevant logs and/or screenshots

added documentation enhancement + 1 deleted label

mentioned in merge request !5 (merged)

closed via merge request !5 (merged)

mentioned in commit a4ee1d7b