Document use of pipenv and whether we should use an alternative

[rdhyee]

Context: Omnibus PR for our consideration 2019.10.04 by rdhyee · Pull Request #746 · ekansa/open-context-py and specifically:

• open-context-py/Pipfile at ry20191004 · rdhyee/open-context-py
• open-context-py/Pipfile.lock at ry20191004 · rdhyee/open-context-py
• use of pipenv in open-context-py/build.yml at ry20191004 · rdhyee/open-context-py

I will flesh out the following common incantation on the built machines.

cd /var/oc-venv
pipenv shell

python manage.py shell

Use something like Poetry - Python dependency management and packaging made easy. instead of pipenv? An analysis: A deeper look into Pipenv and Poetry | Frost's Blog

Right now, pipenv gets the job done...