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README.md

-# Dockerfiles
+# Dockerfiles for base images used in KM3NeT
+
+This repository contains `Dockerfiles` commonly used as base images for
+KM3NeT software.
+
+The images are automatically built and pushed to the `docker.km3net.de`
+repository under the `base` namespace, which means e.g. the image for
+the `Dockerfile` `base/python:3` can used by using the URL
+`docker.km3net.de/base/python:3`.
+
+To start up container and access a shell within, use the usual `docker`
+commands like:
+
+    docker run -it docker.km3net.de/base/centos:7
+
+It is recommended to use these images in your `~/.gitlab-ci.yml` file for
+continuous integrations instead of the public images from DockerHub.