venv: make installed modules visible

[Rich Shepard]

   Activating venv and trying to run the project Python tells me it cannot
find the wxPython4 modules:

Traceback (most recent call last):
   File "./openEDMS.py", line 12, in <module>
     import wx
ModuleNotFoundError: No module named 'wx'

   I've read the Python3 venv standard library doc page (section 28.3)
without seeing how to make installed modules (such as wxPython, psycopg2,
and SQLAlchemy visible in the virtual environment. I suspect that EnvBuilder
is involved but I'm not seeing how to apply this class ... if that's how
modules are made visible in the venv.

   A clue is needed.

Rich