Reinstate kubelets credential provider info

Add (GCR) to list item

Add missing acronyms to list

Rewrite kubelet legacy credential provider

Update section title header

Author: mrgiles

content/en/docs/concepts/containers/images.md

@@ -458,9 +458,22 @@ common use cases and suggested solutions.
 
 If you need access to multiple registries, you can create one secret for each registry.
 
+## Legacy built-in kubelet credential provider
+
+In older versions of Kubernetes, the kubelet had a direct integration with cloud provider credentials.
+This gave it the ability to dynamically fetch credentials for image registries.
+
+There were three built-in implementations of the kubelet credential provider integration:
+ACR (Azure Container Registry), ECR (Elastic Container Registry), and GCR (Google Container Registry).
+
+For more information on the legacy mechanism, read the documentation for the version of Kubenetes that you
+are using. Kubernetes v1.26 through to v{{< skew latestVersion >}} do not include the legacy mechanism, so
+you would need to either:
+- configure a kubelet image credential provider on each node
+- specify image pull credentials using `imagePullSecrets` and at least one Secret
+
 ## {{% heading "whatsnext" %}}
 
 * Read the [OCI Image Manifest Specification](https://github.com/opencontainers/image-spec/blob/master/manifest.md).
 * Learn about [container image garbage collection](/docs/concepts/architecture/garbage-collection/#container-image-garbage-collection).
 * Learn more about [pulling an Image from a Private Registry](/docs/tasks/configure-pod-container/pull-image-private-registry).
-