Add build and run instructions

README.md

@@ -1,2 +1,50 @@
 # bmi-example-c-docker
-The C BMI example, Dockerized
+
+The [C example](https://github.com/csdms/bmi-example-c)
+for the [Basic Model Interface](https://bmi.readthedocs.io),
+dockerized.
+
+## Build an image
+
+Build this example locally with:
+```
+docker build --tag bmi-example-c .
+```
+The image is built on the [condaforge/mambaforge](https://hub.docker.com/r/condaforge/mambaforge) base image.
+The OS is Linux/Ubuntu.
+`conda` and `mamba` are installed in `CONDA_DIR=/opt/conda`.
+The *base* environment is activated,
+and the C BMI example, including the `run_bmiheatc` executable, is installed into it.
+
+## Run a container
+
+Run a container from this image interactively:
+```
+docker run -it bmi-example-c
+```
+This starts a bash shell in the container.
+Run the example program `run_bmiheatc` with a configuration file:
+```bash
+cd /tmp
+echo "1.5, 8.0, 6, 5" > config.txt
+run_bmiheatc config.txt
+```
+View the program's output with:
+```bash
+cat bmiheatc.out
+```
+
+## Developer notes
+
+A versioned, multiplatform image built from this repository is hosted on Docker Hub
+at [csdms/bmi-example-c](https://hub.docker.com/repository/docker/csdms/bmi-example-c-docker/).
+To tag, build, and push an update, run:
+```
+docker buildx build --platform linux/amd64,linux/arm64 -t csdms/bmi-example-c:<tagname> --push .
+```
+where `<tagname>` is, e.g., `0.1` or `latest`.
+
+A user can pull this image from Docker Hub with:
+```
+docker pull csdms/bmi-example-c
+```