Include developer notes for multiplatform build

Author: mdpiper

README.md

@@ -31,6 +31,23 @@ Visiting `http://<hostname>:8888/?token=<token>` in a browser loads JupyterLab,
 * `hostname` is the name of the computer running Docker
 * `token` is the secret token printed in the console
 
+## Developer notes
+
+A versioned, multiplatform image built from this repository is hosted on Docker Hub
+at [csdms/jupyterhub](https://hub.docker.com/repository/docker/csdms/jupyterhub/).
+This image is automatically built and pushed to Docker Hub
+with the [release](./.github/workflows/release.yml) CI workflow.
+The workflow is only run when the repository is tagged.
+To manually build and push an update, run:
+```
+docker buildx build --platform linux/amd64,linux/arm64 -t csdms/jupyterhub:latest --push .
+```
+A user can pull this image from Docker Hub with:
+```
+docker pull csdms/jupyterhub
+```
+optionally with the `latest` tag or with a version tag.
+
 ## What is the CSDMS Workbench?
 
 The CSDMS Workbench is the integrated system of software tools, technologies, and standards developed by CSDMS for building, interfacing, coupling, and running models.