Build docker for arm 64- and 32bit too

.github/workflows/dotnet.yml

@@ -65,16 +65,29 @@ jobs:
         body: Please refer to [this post](https://discourse.openbullet.dev/t/wip-how-to-download-and-start-openbullet-2/29) on the official forum to learn how to launch OpenBullet 2.
 
   push_to_docker:
-    name: Push Docker image to Docker Hub
-    needs: build
-    runs-on: ubuntu-latest
-    steps:
-      - name: Check out the repo
+      name: Push Docker image to Docker Hub
+      needs: build
+      runs-on: ubuntu-latest
+      steps:
+      -
+        name: Checkout
         uses: actions/checkout@v2
-      - name: Push to Docker Hub
-        uses: docker/build-push-action@v1
+      -
+        name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      -
+        name: Login to DockerHub
+        uses: docker/login-action@v1
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
           password: ${{ secrets.DOCKERHUB_TOKEN }}
-          repository: openbullet/openbullet2
-          tags: latest 
+      -
+        name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          push: true
+          platforms: linux/amd64, linux/arm64, linux/arm/v7
+          tags: openbullet/openbullet2:latest