Tidy up devel docker

backend/dev-docker/Dockerfile

@@ -1,5 +1,4 @@
 FROM python:3.8-buster
-RUN mkdir -p /app/dev
 COPY sleep.py /
 CMD [ "python", "/sleep.py" ]
 

backend/dev-docker/sleep.py

@@ -1,9 +1,9 @@
 import time
 import sys
 
+print ("Sleep loop, you should run your script from the console")
 
 while True: 
     # Wait for 5 seconds
-    print('To stderr.', file=sys.stderr)
 
     time.sleep(2)