[Docs] Clarify k8s private registry usage in docs (#3998)

* Clarify k8s private registry auth in docs.

* comments

docs/source/examples/docker-containers.rst

@@ -18,6 +18,10 @@ SkyPilot can run a container either as a task, or as the runtime environment of
 Running Containers as Tasks
 ---------------------------
 
+.. note::
+
+    On Kubernetes, running Docker runtime in a pod is not recommended. Instead, :ref:`use your container as a runtime environment <docker-containers-as-runtime-environments>`.
+
 SkyPilot can run containerized applications directly as regular tasks. The default VM images provided by SkyPilot already have the Docker runtime pre-configured.
 
 To launch a containerized application, you can directly invoke :code:`docker run` in the :code:`run` section of your task.
@@ -173,6 +177,10 @@ Any GPUs assigned to the task will be automatically mapped to your Docker contai
 Private Registries
 ^^^^^^^^^^^^^^^^^^
 
+.. note::
+
+    These instructions do not apply if you use SkyPilot to launch on Kubernetes clusters. Instead, see :ref:`Using Images from Private Repositories in Kubernetes<kubernetes-custom-images-private-repos>` for more.
+
 When using this mode, to access Docker images hosted on private registries,
 you can provide the registry authentication details using :ref:`task environment variables <env-vars>`:
 

docs/source/reference/kubernetes/kubernetes-getting-started.rst

@@ -119,6 +119,8 @@ Once your cluster administrator has :ref:`setup a Kubernetes cluster <kubernetes
     $ kubectl config set-context --current --namespace=mynamespace
 
 
+.. _kubernetes-custom-images:
+
 Using Custom Images
 -------------------
 By default, we use and maintain a SkyPilot container image that has conda and a few other basic tools installed.
@@ -140,6 +142,8 @@ Your image must satisfy the following requirements:
 
     If your cluster runs on non-x86_64 architecture (e.g., Apple Silicon), your image must be built natively for that architecture. Otherwise, your job may get stuck at :code:`Start streaming logs ...`. See `GitHub issue <https://github.com/skypilot-org/skypilot/issues/3035>`_ for more.
 
+.. _kubernetes-custom-images-private-repos:
+
 Using Images from Private Repositories
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 To use images from private repositories (e.g., Private DockerHub, Amazon ECR, Google Container Registry), create a `secret <https://kubernetes.io/docs/tasks/configure-pod-container/pull-image-private-registry/#create-a-secret-by-providing-credentials-on-the-command-line>`_ in your Kubernetes cluster and edit your :code:`~/.sky/config.yaml` to specify the secret like so: