update kubernetes.io/os description as it can also be used in pod labels

Author: pacoxu

content/en/docs/reference/labels-annotations-taints/_index.md

@@ -116,10 +116,16 @@ The Kubelet populates this with `runtime.GOARCH` as defined by Go. This can be h
 
 Example: `kubernetes.io/os: "linux"`
 
-Used on: Node
+Used on: Node, Pod
 
 The Kubelet populates this with `runtime.GOOS` as defined by Go. This can be handy if you are mixing operating systems in your cluster (for example: mixing Linux and Windows nodes).
 
+When the `kubernetes.io/os` label value for a Pod does not match the label value on a Node,
+the kubelet on the node will not admit the Pod. However, this is not taken into account by
+the kube-scheduler. Alternatively, the kubelet refuses to run a Pod where you have specified a Pod OS, if
+this isn't the same as the operating system for the node where that kubelet is running. Just
+look for [Pods OS](/docs/concepts/workloads/pods/#pod-os) for more details.
+
 ### kubernetes.io/metadata.name
 
 Example: `kubernetes.io/metadata.name: "mynamespace"`