Raised a more helpful ImportError message in manage.py template.

if __name__ == "__main__":

    os.environ.setdefault("DJANGO_SETTINGS_MODULE", "{{ project_name }}.settings")

    try:

        from django.core.management import execute_from_command_line

    except ImportError:

        raise ImportError(

            "Couldn't import Django. Are you sure it's installed and available "

            "on your PATH environment variable? Did you forget to activate a "

            "virtual environment?"

        )

    execute_from_command_line(sys.argv)