docs(demos): tell operators to update both halves of the TCPXO pair

The manifest header told the reader to update only the plugin tag when their
cluster runs a different installer version. Following it leaves both daemon
references untouched, recreating the mismatched pair this change exists to fix.

State the coupling, name the pinned pair, and say to update both images, so the
manifest carries the same guidance the integrator doc already gives.

Also correct the lookup: the installer image lives in initContainers, not
containers, so the previous jsonpath returned empty.

Signed-off-by: Yuan Chen <yuanchen97@gmail.com>

Author: yuanchen8911

demos/workloads/training/gke-nccl-test-tcpxo.yaml

@@ -32,11 +32,17 @@
 #   - GPU Operator with driver.enabled=false (GKE COS manages drivers)
 #
 # Image version note:
-#   The nccl-test container image must match the cluster's installed TCPXO
-#   plugin version. Check with:
+#   Google ships the plugin installer and the tcpxo-daemon as a coupled release
+#   pair; running a mismatched pair is unsupported. This manifest is pinned to
+#   v1.0.15 (nccl-plugin-gpudirecttcpx-dev) with v1.0.21 (tcpgpudmarxd-dev),
+#   matching the installer the AICR recipe deploys.
+#
+#   If your cluster runs a different installer version, check it with:
 #     kubectl get ds nccl-tcpxo-installer -n kube-system \
-#       -o jsonpath='{.spec.template.spec.containers[?(@.name=="nccl-tcpxo-installer")].image}'
-#   Then update the nccl-plugin-gpudirecttcpx-dev tag below to match.
+#       -o jsonpath='{.spec.template.spec.initContainers[?(@.name=="nccl-tcpxo-installer")].image}'
+#   then update BOTH images below to that installer's pair, per Google's
+#   release table: https://github.com/GoogleCloudPlatform/container-engine-accelerators/blob/master/gpudirect-tcpxo/README.md
+#   Updating only one half recreates the mismatch this pairing exists to avoid.
 #
 # Usage:
 #   kubectl create ns nccl-test