add info that user need to be in docker group

README.rst

@@ -121,6 +121,8 @@
 
   apt install python-docker python-psycopg2 python-requests
 
+Your user also needs to be in the docker group.
+
 It expect the configuration file (`setup.cfg`_) to have the following keys:
 
 - ``modules``: list of directories and files to include