Add the accepted types for imagePullSecrets

Author: Rishit-dagli

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

@@ -275,6 +275,8 @@ in private registries.
 {{< /note >}}
 
 Kubernetes supports specifying container image registry keys on a Pod.
+`imagePullSecrets` must all be in the same namespace as the Pod. The referenced
+Secrets must be of type `kubernetes.io/dockercfg` or `kubernetes.io/dockerconfigjson`.
 
 #### Creating a Secret with a Docker config
 
@@ -303,7 +305,8 @@ so this process needs to be done one time per namespace.
 #### Referring to an imagePullSecrets on a Pod
 
 Now, you can create pods which reference that secret by adding an `imagePullSecrets`
-section to a Pod definition.
+section to a Pod definition. Each item in the `imagePullSecrets` array can only
+reference a Secret in the same namespace.
 
 For example: