Add release ci workflow

.github/workflows/release.yml

@@ -0,0 +1,35 @@
+name: Docker Hub
+
+on:
+  push:
+    tags:
+      - 'v[0-9]+.[0-9]+.[0-9]+'
+      - '!v[0-9]+.[0-9]+.[0-9]+[ab][0-9]+'
+
+jobs:
+
+  build-and-push:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Get version
+        id: vars
+        run: echo "version=${GITHUB_REF:11}" >> $GITHUB_OUTPUT
+
+      - name: Set up Docker buildx
+        uses: docker/setup-buildx-action@v3
+        with:
+          platforms: linux/amd64,linux/arm64
+
+      - name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+
+      - name: Build and push
+        uses: docker/build-push-action@v6
+        with:
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ github.repository }}:latest,${{ github.repository }}:${{ steps.vars.outputs.version }}

README.md

@@ -38,12 +38,9 @@ cat bmiheatc.out
 
 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`.
-
+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.
 A user can pull this image from Docker Hub with:
 ```
 docker pull csdms/bmi-example-c