Add comment for manual login step in publish script

Author: opajonk

.github/workflows/ci.yaml

@@ -56,5 +56,6 @@ jobs:
           # Instead, we use the publish script which pushes the correct container (residing in src/s-core-devcontainer).
           push: "never"
           runCmd: |
+            # manually login to ghcr.io for publishing
             echo "${{ secrets.GITHUB_TOKEN }}" | docker login ghcr.io -u ${{ github.actor }} --password-stdin
             ./scripts/publish.sh "latest"