Setup repo for usual Sphinx location:
* content lives in doc/source
* Add tox.ini for building with linter and docs job
* Add doc/source/conf.py for Sphinx
* Add index file to build a manual
* Add jobs for Zuul; note that tox-linters is non-voting for now, fixing
issues can be done as followup.
The docs job has Sphinx warnings disabled, this will be a followup as
* Add .gitignore for usual build artefacts
To be able to merge anything, we need some jobs. Add the noop-jobs that
don't test anything but allow merging.
Those can be replaced later with real jobs.