Update docs

fibonaccifit/README.md

 # Setup
 
-The Docker image needs to be built with the following command:
+For local development, the Docker image can be built with the following command:
 
     docker build --no-cache -t fibonaccifit -f Dockerfile .
     
 Each time the `Project.toml` is changed due to modified dependencies,
 the `fibonaccifit` Docker image needs to be rebuilt using the command
 above.
+
+To use the local image, change the `docker-compose.yml` to point to
+`fibonaccifit` (or whatever tag was used for the image) instead of the one in
+the [km3mon Container
+Registry](https://git.km3net.de/km3py/km3mon/container_registry).