add comments to example github actions file

Author: chendaniely

book/lectures/120-containerization-3.qmd

@@ -326,6 +326,8 @@ For that last step to happen,
 the code owner's DockerHub credentials must be stored in the GitHub repository
 as [GitHub repository secrets](https://docs.github.com/en/actions/security-for-github-actions/security-guides/using-secrets-in-github-actions).
 
+Example .`github/workflows/docker-publish.yml` file:
+
 ```yaml
 # Publishes docker image, pinning actions to a commit SHA,
 # and updating most recently built image with the latest tag.
@@ -339,6 +341,7 @@ on:
   push:
     paths:
       - 'Dockerfile'
+      - .github/workflows/docker-publish.yml # or whatever you named the file
       - 'conda-linux-64.lock'
 
 jobs:
@@ -352,14 +355,14 @@ jobs:
       - name: Log in to Docker Hub
         uses: docker/login-action@v3
         with:
-          username: ${{ secrets.DOCKER_USERNAME }}
-          password: ${{ secrets.DOCKER_PASSWORD }}
+          username: ${{ secrets.DOCKER_USERNAME }} # do not change, add as secret
+          password: ${{ secrets.DOCKER_PASSWORD }} # do not change, add as secret
 
       - name: Extract metadata (tags, labels) for Docker
         id: meta
         uses: docker/metadata-action@v5
         with:
-          images: ttimbers/dsci522-dockerfile-practice
+          images: ttimbers/dsci522-dockerfile-practice # change to your image
           tags: |
             type=raw, value={{sha}},enable=${{github.ref_type != 'tag' }}
             type=raw, value=latest