Clarify MIG, mention private CI registry

Author: empovit

demo/clusters/openshift/README.md

@@ -4,7 +4,7 @@ This document explains the differences between deploying the NVIDIA DRA driver o
 
 ## Prerequisites
 
-Install a recent build of OpenShift 4.16 (e.g. 4.16.0-ec.3). You can obtain an IPI installer binary (`openshift-install`) from the [Release Status](https://amd64.ocp.releases.ci.openshift.org/) page, or use the Assisted Installer to install on bare metal. Refer to the [OpenShift documentation](https://docs.openshift.com/container-platform/4.15/installing/index.html) for different installation methods.
+Install a recent build of OpenShift 4.16 (e.g. 4.16.0-ec.4). You can use the Assisted Installer to install on bare metal, or obtain an IPI installer binary (`openshift-install`) from the [Release Status](https://amd64.ocp.releases.ci.openshift.org/) page. Note that a development version of OpenShift requires access to [an internal CI registry](https://docs.ci.openshift.org/docs/how-tos/use-registries-in-build-farm/) in the pull secret. Refer to the [OpenShift documentation](https://docs.openshift.com/container-platform/4.15/installing/index.html) for different installation methods.
 
 ## Enabling DRA on OpenShift
 
@@ -132,6 +132,13 @@ Enabled MIG Mode for GPU 00000000:0A:00.0
 All done.
 ```
 
-Make sure to stop everything that may hold the GPU before enabling MIG. Otherwise you will see a warning, and the MIG status will have an asterisk (i.e. `Enabled*`), meaning that the setting could not be applied.
+Make sure to stop everything that may hold the GPU before enabling MIG. For example, the DCGM and DCGM Exporter of the NVIDIA GPU Operator are likely to prevent the MIG setting from being applied. Disable them in the operator's cluster policy if you are planning on using MIG:
+
+```console
+Warning: MIG mode is in pending enable state for GPU 00000001:00:00.0:In use by another client
+00000001:00:00.0 is currently being used by one or more other processes (e.g. CUDA application or a monitoring application such as another instance of nvidia-smi). Please first kill all processes using the device and retry the command or reboot the system to make MIG mode effective.
+```
+
+If the MIG status is marked with an asterisk (i.e. `Enabled*`), it means that the setting could not be fully applied and you may need to reboot the node.
 
 No MIG devices must be pre-configured on the GPU if it is going to be used with DRA — the DRA driver will configure MIG automatically on the fly.