update labels (#3925) (#2439)

Signed-off-by: Modular Magician <[email protected]>

Author: modular-magician

.changelog/3925.txt

@@ -0,0 +1,2 @@
+```release-note:none
+```

website/docs/r/container_cluster.html.markdown

@@ -564,7 +564,8 @@ The `node_config` block supports:
 * `image_type` - (Optional) The image type to use for this node. Note that changing the image type
     will delete and recreate all nodes in the node pool.
 
-* `labels` - (Optional) The Kubernetes labels (key/value pairs) to be applied to each node.
+* `labels` - (Optional) The Kubernetes labels (key/value pairs) to be applied to each node. The kubernetes.io/ and k8s.io/ prefixes are
+    reserved by Kubernetes Core components and cannot be specified.
 
 * `local_ssd_count` - (Optional) The amount of local SSD disks that will be
     attached to each cluster node. Defaults to 0.