Test/document `gulp` usage in non-Docker dev

[tobiasmcnulty]

It looks like our gulpfile.js is missing the code that actually calls runServer(), and possibly other things. We should compare it again to the django-cookiecutter template, update as needed, and document the commands one needs to run to get static assets building locally.

As a temporary workaround, you can run gulp in a separate shell (but you'll still need to run and access python manage.py runserver manually on port 8000, not port 3000).

A/C:

• [ ] Port 3000 does not render the site before this fix
• [ ] Port 3000 renders the site after the fix

[ronardcaktus]

Moving this to the backlog because I am running the application in docker and therefore can't access port 3000.

[tobiasmcnulty]

Obsolete since we are moving to webpack. /CC @janelle-caktus