add workflow file to build p2k16-label docker image, part of fixing #19.

.github/workflows/docker-image-p2k16-label.yml

@@ -0,0 +1,37 @@
+name: Build and push p2k16-label docker image
+
+on:
+  release:
+    types: [published]
+
+jobs:
+  build-and-push-docker-image:
+    runs-on: ubuntu-latest
+
+    # steps to perform in job
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Login to Github Packages
+        uses: docker/login-action@v1
+        with:
+          registry: ghcr.io
+          username: ${{ github.actor }}
+          password: ${{ secrets.GITHUB_TOKEN }}
+
+      - name: Get the version
+        id: vars
+        run: echo ::set-output name=tag::$(echo ${GITHUB_REF:10})
+
+      - name: Build image and push to  GitHub Container Registry
+        uses: docker/build-push-action@v2
+        with:
+          # relative path to the place where source code with Dockerfile is located
+          context: ./p2k16-label
+          # Note: tags has to be all lower-case
+          tags: |
+            ghcr.io/bitraf/p2k16-label:${{steps.vars.outputs.tag}}
+            ghcr.io/bitraf/p2k16-label:latest
+          # build on feature branches, push only on main branch
+          push: ${{ github.ref == 'refs/heads/main' }}