Improve documention in publish.yml, fix docker image tag names

Author: manics

.github/workflows/publish.yml

@@ -28,6 +28,11 @@ jobs:
     steps:
       - uses: actions/checkout@v2
 
+      # Setup docker to build for multiple platforms (requires qemu).
+      # See:
+      # https://github.com/docker/build-push-action/tree/v2.3.0#usage
+      # https://github.com/docker/build-push-action/blob/v2.3.0/docs/advanced/multi-platform.md
+
       - name: Set up QEMU
         uses: docker/setup-qemu-action@v1
 
@@ -43,13 +48,19 @@ jobs:
           password: ${{ secrets.DOCKERHUB_TOKEN }}
 
       # https://github.com/manics/action-major-minor-tag-calculator-test
+      # If this is a tagged build this will return additional parent tags.
+      # E.g. 1.2.3 is expanded to Docker tags
+      # [{prefix}:1.2.3, {prefix}:1.2, {prefix}:1, {prefix}:latest] unless
+      # this is a backported tag in which case the newer tags aren't updated.
+      # For branches this will return the branch name.
+      # If GITHUB_TOKEN isn't available (e.g. in PRs) returns no tags [].
       - name: Get list of tags
         id: gettags
         # TODO: Move to org?
         uses: manics/action-major-minor-tag-calculator@main
         with:
           githubToken: ${{ secrets.GITHUB_TOKEN }}
-          prefix: "manics/action-major-minor-tag-calculator-test:"
+          prefix: "jupyterhub/configurable-http-proxy:"
 
       - name: Display tags
         run: echo "Docker tags ${{ steps.gettags.outputs.tags }}"
@@ -59,4 +70,6 @@ jobs:
         with:
           platforms: linux/amd64,linux/arm64
           push: ${{ startsWith(github.ref, 'refs/tags/') }}
+          # tags parameter must be a string input so convert `gettags` JSON
+          # array into a comma separated list of tags
           tags: ${{ join(fromJson(steps.gettags.outputs.tags)) }}