Providing latest tag, updating README.md.

Dockerfile

-FROM fedora:31
+FROM fedora:latest
 
 RUN dnf upgrade -y && \
     dnf install -y \

Makefile

 CONTAINER_NAME = registry.hzdr.de/pape58/slurm-in-docker
-CONTAINER_TAG  = fedora-31
-CONTAINER      = ${CONTAINER_NAME}:${CONTAINER_TAG}
+CONTAINER_TAGS = latest fedora-latest
+CONTAINER      = $(CONTAINER_NAME):$(firstword $(CONTAINER_TAGS))
+CONTAINER_LIST = $(foreach tag,$(CONTAINER_TAGS),$(CONTAINER_NAME):$(tag))
 
 .PHONY: build push run
 
 build: Dockerfile docker-entrypoint.sh
-	docker build -t ${CONTAINER} .
+	docker build $(foreach c,$(CONTAINER_LIST),-t $(c)) .
 
 push: build
-	docker push ${CONTAINER}
+	docker push $(CONTAINER_LIST)
 
 run: build
-	docker run -ti --rm ${CONTAINER}
+	docker run -ti --rm $(CONTAINER)

README.md

@@ -13,42 +13,52 @@ hyperthreading, ...). The *cluster* (if you want to call your single node that)
 When you start the container, the services are already up and running. You will be greeted by a Bash
 shell running as `root`.
 
-## Building and running the container
-
-If you have Docker set up on your system, you can easily start the container by executing
-`make run`. This will automatically build and tag the image for you. The first build may take a few
-minutes.
-
-The default target for make is `build`. This will build the container using the name and tag
-specified at the top of the Makefile. If you wish to give the container a different name, you can
-pass it to `make` as an argument, e.g. `make CONTAINER=slurm`.
-
-## Just running the container
+## Running the container
 
 If you don't want to build the container yourself, you can pull it from HZDR's registry. (Remember
 to log in and out!)
 
 ```bash
 docker login registry.hzdr.de
-docker pull registry.hzdr.de/pape58/slurm-in-docker:fedora-31
+docker pull registry.hzdr.de/pape58/slurm-in-docker
 docker logout registry.hzdr.de
 ```
 
 To run the container use this command:
 
 ```bash
-docker run -ti --rm registry.hzdr.de/pape58/slurm-in-docker:fedora-31
+docker run -ti --rm registry.hzdr.de/pape58/slurm-in-docker
 ```
 
 The image is updated weekly.
 
+## Building the container
+
+If you have Docker set up on your system, you can easily build the container by executing `make`.
+This will run the default target `build` which builds and tags the image for you. The first build
+may take a few minutes.
+
+The default name of the container is `registry.hzdr.de/pape58/slurm-in-docker`. If you want to
+choose a shorter name, you can pass it as an argument when building the container, e.g.
+
+```bash
+make CONTAINER_NAME=slurm
+```
+
+Verify the build worked:
+
+```bash
+docker image ls
+```
+
 ## Using it in your CI job
 
-... is as easy as
+... is as easy as specifying `image: registry.hzdr.de/pape58/slurm-in-docker`. GitLab will pull it
+from the registry for you and place your job inside of a new container. Here is an example job:
 
 ```yml
 my_job:
-    image: registry.hzdr.de/pape58/slurm-in-docker:fedora-31
+    image: registry.hzdr.de/pape58/slurm-in-docker
     script:
         - srun -n 2 hostname
 ```
@@ -56,10 +66,10 @@ my_job:
 ## Running other programs
 
 You can pass any program name to the container. At the moment, there are not a lot of programs
-installed on it, though. Feel free to write an issue or provide a merge request if you have any
+installed on it, though. Feel free to submit an issue or a merge request if you have any
 suggestions.
 
 ```bash
-docker run -it --rm registry.hzdr.de/pape58/slurm-in-docker:fedora-31 ps faux
+docker run -ti --rm registry.hzdr.de/pape58/slurm-in-docker ps aux
 ```