ci: build multiarch docker images

Author: bchew

.github/workflows/docker.yml

@@ -16,6 +16,12 @@ jobs:
     steps:
       - name: Check out the repo
         uses: actions/checkout@v2
+
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
 
       - name: Log in to Docker Hub
         uses: docker/login-action@v1
@@ -33,6 +39,7 @@ jobs:
         uses: docker/build-push-action@v2
         with:
           context: .
+          platforms: linux/amd64,linux/arm64
           push: true
           tags: ${{ steps.meta.outputs.tags }}
           labels: ${{ steps.meta.outputs.labels }}