Another try at PROJECT_ROOT and PROJECT_PATH

PROJECT_ROOT is the top dir containing things for this project,
PROJECT_PATH is a subdir with the settings, wsgi.py, etc.

Added some comments to explain.

Wrote `PROJECT_PATH = os.path.join(PROJECT_ROOT, '{{ project_name }}')`
instead of `PROJECT_PATH = os.path.dirname(__file__)` because I thought
it made it a little clearer on reading it which directory we were
talking about, but it would work either way.