ci(actions): add workflow for publishing images to DockerHub

Including an arm64 build

.github/workflows/build.yml

@@ -0,0 +1,33 @@
+name: Build
+
+on:
+  push:
+    branches:
+      - main
+      - master
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        elixir:
+          - "1.9"
+          - "1.10"
+    steps:
+      - uses: actions/checkout@v2
+      - uses: docker/setup-qemu-action@v1
+      - uses: docker/setup-buildx-action@v1
+      - uses: docker/login-action@v1
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      - uses: docker/build-push-action@v2
+        with:
+          context: ${{ matrix.elixir }}
+          push: true
+          tags: articulate/articulate-elixir:${{ matrix.elixir }}
+          platforms: linux/amd64,linux/arm64/v8
+          cache-from: type=registry,ref=articulate/articulate-elixir:${{ matrix.elixir }}
+          cache-to: type=inline