Added comment in jupyterhub_config.py

Hope this helps fix issues like in #8

Author: defeo

jupyterhub/jupyterhub_config.py

@@ -1,3 +1,14 @@
+# JupyterHub configuration
+#
+## If you update this file, do not forget to delete the `jupyterhub_data` volume before restarting the jupyterhub service:
+##
+##     docker volume rm jupyterhub_jupyterhub_data
+##
+## or, if you changed the COMPOSE_PROJECT_NAME to <name>:
+##
+##    docker volume rm <name>_jupyterhub_data
+##
+
 import os
 
 ## Generic