rename docker-compose files and remove unused network "app"

the default docker compose file should be minimal and easy to read as docker-compose.yml

other docker-compose variants for typical setup should be named as:
 docker-compose.<variant>.yml

this way one could use e.g. `docker compose -f docker-compose.traefik.yml up` to
start the variant for traefik. (mind keeping the file extension)

and fixed a typo the README.md

README.md

@@ -50,5 +50,9 @@ docker compose build
 - run
 
 ```
-docker compose build
+docker compose up
+
+# or variant with traefik labels:
+
+docker compose -f docker-compose.traefik.yml up
 ```