Add helpful note about gmxpai docker notebook server.

Per Joe's comment on https://gerrit.gromacs.org/c/gromacs/+/11502, it
was not clear where the notebook files live or how they may / may not
change. An extra snippet in the README.md may be helpful.

Change-Id: Ifd7b68ebf58fb3f2c3bed50f3267980358ffc047

diff --git a/python_packaging/docker/README.md b/python_packaging/docker/README.md
index b18aca01c9bd5715384a0d0497b55c61353ba7a8..73efcc7a4e763e4ed982f70fb76648a0c8b3d5ad 100644 (file)
--- a/python_packaging/docker/README.md
+++ b/python_packaging/docker/README.md
@@ -47,6 +47,15 @@ The image should be tagged according to the functionality it is intended to demo
 
 ## Running
 
+**Warning:** The `--rm` flag tells Docker to remove the container after the
+process completes. This prevents unnamed containers from consuming more disk
+space on the host with each `run`.
+
+Alternatively, replace `--rm` with `--name containername` to save a named copy
+of the container and consider using `commit`ing snapshots of the container.
+
+Refer to Docker documentation for details.
+
 ### ci.dockerfile
 
 The `entrypoint.sh` script activates the python venv and wraps commands in a `bash` `exec`.
@@ -83,6 +92,12 @@ easy access to a Jupyter notebook server running in the docker container's
 
     docker run --rm -ti -p 8888:8888 gmxapi/notebook
 
+Note that, when run with `--rm`, changes made to files in the container will be
+lost when `docker run` completes.
+To preserve work in a notebook run this way,
+download the `ipynb` through theJupyter web interface
+(such as when updating the examples in the repository).
+
 ## Automation
 
 *TODO: Update this section as Jenkins infrastructure evolves.*