Update migrate_dc.md

docs/migrate_dc.md

@@ -35,6 +35,11 @@ systemctl start docker
 pip install docker-compose
 mkdir /etc/docker-compose/tower -p
 ```
+### Adding a user to the docker group 
+```
+usermod -a -G docker &user
+newgrp docker
+```
 
 ## Migrate current installation