title: Is possible to add a python path with pipenv?
body: <p>I have some old python projects that are NOT packaged (no setup.py) I need to access them.
  Till now I was using buildout where I can specify a python path in buildout.cfg.
  I would like to switch to pipenv : how can I specify an arbitrary python path with pipenv so I can import my unpackaged projects ?</p>