diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 8e6f2b1..26e7693 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -29,7 +29,7 @@ jobs:
       -
         name: Build docker builder-image
         if: steps.cache-docker.outputs.cache-hit != 'true'
-        uses: docker/build-push-action@v4
+        uses: docker/build-push-action@v5
         with:
           context: .
           file: builder.Dockerfile
diff --git a/builder.Dockerfile b/builder.Dockerfile
index 0fad747..c12d46d 100644
--- a/builder.Dockerfile
+++ b/builder.Dockerfile
@@ -1,3 +1,7 @@
+# update the base_tag to the version of the base image
+# e.g., "bullseye" is currently (2024-02) still the latest version for vscode devcontainers:
+# https://hub.docker.com/_/microsoft-vscode-devcontainers
+
 ARG base_tag=bullseye
 ARG base_img=mcr.microsoft.com/vscode/devcontainers/base:dev-${base_tag}
 # ARG base_img=debian:${base_tag}
@@ -8,6 +12,9 @@ FROM --platform=linux/amd64 ${base_img} AS builder-install
 # you can determine the installed version with `apt-cache policy <list of packages>` and fix
 # the version to install with <package>=<version> in the list below.
 
+# notice that ruby is being installed for ceedling and would otherwise most likely not be needed
+# https://www.throwtheswitch.org/ceedling
+
 RUN apt-get update --fix-missing && apt-get -y upgrade
 RUN apt-get install -y --no-install-recommends \
     apt-utils \