Merge remote-tracking branch 'origin/doc-updates' into integration_2025_w33 (!3590)

Improve MAC docs for MCS and docker for BuildKit usage

See commits for details. The first one is for fixing an omission in
!3281, the second to clarify docker build usage.

Closes: #973

docker/README.md

@@ -91,6 +91,24 @@ For more details regarding the build on an Openshift Cluster, see [OpenShift REA
 * `docker-ce` installed
 * Pulling `ubuntu:jammy` from DockerHub
 
+The docker files in this directory rely on [automatic Docker platform
+arguments](https://docs.docker.com/reference/dockerfile/#automatic-platform-args-in-the-global-scope)
+`TARGETARCH` and `TARGETPLATFORM` to be defined. This is the case when using
+[BuildKit](https://docs.docker.com/build/buildkit/), which is automatically
+enabled in newer (v23.0+) docker versions.
+
+If you are running an older version of docker that does not have BuildKit
+enabled and do not wish to upgrade to a newer docker version, you have two
+possibilities:
+
+1. [Enable BuildKit](https://docs.docker.com/build/buildkit/#getting-started)
+   when building: `DOCKER_BUILDKIT=1 docker build ...`
+2. You should be able to define these variables manually.
+   - x86: `docker build --build-arg TARGETARCH=amd64 --build-arg
+     TARGETPLATFORM=linux/amd64 ...`
+   - arm: `docker build --build-arg TARGETARCH=arm64 --build-arg
+     TARGETPLATFORM=linux/arm64 ...`
+
 ## 3.2. Building the shared images ##
 
 There are two shared images: one that has all dependencies, and a second that compiles all targets (eNB, gNB, [nr]UE).