Add a note about upgrading docker version

Dockerfile

@@ -1,5 +1,20 @@
-# Keep in sync with default Dockerfile
-FROM node:22.12.0-slim@sha256:a4b757cd491c7f0b57f57951f35f4e85b7e1ad54dbffca4cf9af0725e1650cd8
+# When updating the version of the base container, please use the
+# SHA256 listed under 'Index digest' on Docker Hub,
+# not the 'Manifest digest'.
+#
+# This ensures that when pulling the container, Docker will detect
+# the platform and pull the correct image (if it exists)
+#
+# Alternate way of determining the Index digest using the docker CLI.
+#
+# $ docker buildx imagetools inspect node:22.12.0-slim
+# Name:      docker.io/library/node:22.12.0-slim
+# MediaType: application/vnd.oci.image.index.v1+json
+# Digest:    sha256:a4b757cd491c7f0b57f57951f35f4e85b7e1ad54dbffca4cf9af0725e1650cd8
+# And use this digest in FROM
+ARG base_sha=a4b757cd491c7f0b57f57951f35f4e85b7e1ad54dbffca4cf9af0725e1650cd8
+
+FROM node:22.12.0-slim@sha256:${base_sha}
 
 ENV NODE_OPTIONS=--max-old-space-size=4096