Change error message from "runpylint" to "run pylint"

[john-sandall]

There's a small (but potentially misleading for novices) typo in Django was not configured. For more information runpylint --load-plugins=pylint_django --help-msg=django-not-configured.

This should be Django was not configured. For more information runpylint --load-plugins=pylint_django --help-msg=django-not-configured`.

This was also referenced in #306 (but was not the actual issue being reported).

Environment Versions

• OS Type = macOS
• Python version: $ python -V
  • Python 3.6.11
• pip version: $ pip --version
pip 21.0.1
• pylint-django version: pip freeze | grep "pylint-django"
pylint-django==2.4.2