Clarify installation instructions

Author: benrencher

docs/usage.rst

@@ -7,7 +7,7 @@ Installation
 1. Install ``django-simple-captcha`` via pip_: ``pip install  django-simple-captcha``
 2. Add ``captcha`` to the ``INSTALLED_APPS`` in your ``settings.py``
 3. Run ``python manage.py migrate``
-4. Add an entry to your ``urls.py``::
+4. Add an entry to your ``urls.py`` (import ``include`` from ``django.urls``)::
 
         urlpatterns += [
             path('captcha/', include('captcha.urls')),