[Doc] Add a general description for Compose template

template/docker-compose.yml

 version: "3.7"
 
+# This is an example with common values.
+# Depending on the context, you may no have
+# to use them all : maybe you don't need
+# volumes of Traefik, feel free to remove
+# everything you don't need or understand
+# to suit your needs.
+# Don't hesitate to ask to the tech team.
+
 volumes:
   # Declaration of Docker volume
   # Also use a name so that Docker Compose does not add