documentation bug/ unittest mis-match: unittest assume global installation

[AaronK]

Going through and testing the documentation, I noticed that the unittest discover instructions assume that we have a global installation.

If we follow the Developer guide, we might end up with a .venv installation.
(following: https://intelmq.readthedocs.io/en/develop/dev/guide.html)

Result:

(.venv) aaron@bee:/opt/dev_intelmq$ sudo -u intelmq python3 -m unittest discover
sudo: unknown user intelmq