Add workflow to test the build of the image (#39)

.github/workflows/build.yaml

@@ -0,0 +1,20 @@
+name: Build
+
+on:
+  pull_request:
+    branches:
+      - main
+
+jobs:
+  build:
+    name: Build image
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/[email protected]
+
+      - name: Build
+        uses: docker/[email protected]
+        with:
+          context: .
+          push: false
+          tags: "ghcr.io/${{ github.repository_owner }}/private-demo:pr-${{ github.event.number }}"