Update quickstart.md

Add the 'django' package to the pip install command, as per the comment/description above said command.

docs/tutorial/quickstart.md

@@ -15,7 +15,7 @@ Create a new Django project named `tutorial`, then start a new app called `quick
     source env/bin/activate  # On Windows use `env\Scripts\activate`
 
     # Install Django and Django REST framework into the virtual environment
-    pip install djangorestframework
+    pip install django djangorestframework
 
     # Set up a new project with a single application
     django-admin startproject tutorial .  # Note the trailing '.' character