docs: tweak quickstart example

docs/narr/install/quickstart.rst

@@ -116,8 +116,7 @@ invoke other app/handler logic::
    # invoke secondary handler to make new user account
    auth = app.get_auth_handler()
    user = auth.make_user(session=session, username='barney')
-
-   # commit changes to DB
+   assert isinstance(user, model.User)
    session.add(user)
    session.commit()