Edit to be more affirmative

docs/source/usage.rst

@@ -63,8 +63,8 @@ you should put the following in ``requirements.txt`` or ``environment.yml``::
 
   jupyterhub==0.8.*
 
-In your JupyterHub configuration, you may also need to pass a command to the Spawner
-to run ``jupyterhub-singleuser``, for instance if using ``DockerSpawner``::
+If your instance of JupyterHub uses ``DockerSpawner``, you will need to set its
+command to run ``jupyterhub-singleuser``::
 
   c.DockerSpawner.cmd = ['jupyterhub-singleuser']