Build multi-arch Docker image (add arm64 via QEMU)

Author: HDash

.github/workflows/docker-publish.yml

@@ -1,7 +1,8 @@
 name: 🐳 Build and publish Docker image
 
 # Publishes ghcr.io/neurogenomics/microglia-sorting:latest on every push to main.
-# Can also be triggered by hand from the Actions tab.
+# The image is multi-arch (linux/amd64 + linux/arm64); the arm64 leg is built
+# under QEMU emulation. Can also be triggered by hand from the Actions tab.
 on:
   push:
     branches:
@@ -15,13 +16,17 @@ env:
 jobs:
   build-and-push:
     runs-on: ubuntu-latest
+    timeout-minutes: 360          # arm64 under QEMU is slow; allow the max
     permissions:
       contents: read
       packages: write
     steps:
       - name: Check out repository
         uses: actions/checkout@v4
 
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v4
+
       - name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v4
 
@@ -37,4 +42,5 @@ jobs:
         with:
           context: .
           push: true
+          platforms: linux/amd64,linux/arm64
           tags: ${{ env.REGISTRY }}/${{ env.IMAGE_NAME }}:latest