improve instructions for local docker test

README.md

@@ -17,10 +17,21 @@ TBD
 
 ### Docker
 
-For advanced users only: If you happen to have Docker installed, you can start a local dockerized JupyterLab with
+If you happen to have Docker installed, you can start a local dockerized JupyterLab for testing your profile:
 
 ```bash
-docker run --name='jupyter-example-profile' --rm -it -p 8888:8888 registry.git-ce.rwth-aachen.de/jupyter/profiles/example:master
+# Navigate to your local clone of this repo
+cd path/to/example-profile
+
+# Login to the RWTH GitLab Docker registry
+#  (required for pulling the base image)
+docker login registry.git.rwth-aachen.de
+
+# Build the Docker image
+docker build --tag jupyter-example-profile .
+
+# Run the Docker image
+docker run --name='jupyter-example-profile' --rm --interactive --tty --publish 8888:8888 --volume ${HOME}:/home/jovyan jupyter-example-profile
 ```
 
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