additional library was required for venv_dev

[stt08]

Solution was found on https://stackoverflow.com/a/14424226

The documentation should contain libpq-dev dependency

FIXES #4258

[whisperity]

The guide in the README is for venv, not venv_dev. I don't think we should force dependencies on users that only want to use CodeChecker, as per following the guide, that are not required for the proper function of the deployment package.

[dkrupp]

The guide in the README is for venv, not venv_dev. I don't think we should force dependencies on users that only want to use CodeChecker, as per following the guide, that are not required for the proper function of the deployment package.

The document is also about venv_dev see this note above:
# NOTE: if you want to develop CodeChecker, use the venv_dev` target instead

of venv.`

So I think we could extend the note with this

In case of venv_dev and Ubuntu 23, install an additional library:

[dkrupp]

Please mention that this extra dependency is only needed for venv_dev