YARN-6012. Remove node label (removeFromClusterNodeLabels) document is missing (Contributed by Ying Zhang via Daniel Templeton)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-site/src/site/markdown/NodeLabel.md

@@ -20,6 +20,7 @@ YARN Node Labels
 * [Configuration](#Configuration)
     * [Setting up ResourceManager to enable Node Labels](#Setting_up_ResourceManager_to_enable_Node_Labels)
     * [Add/modify node labels list to YARN](#Add/modify_node_labels_list_to_YARN)
+    * [Remove node labels from YARN](#Remove_node_labels_from_YARN)
     * [Add/modify node-to-labels mapping to YARN](#Add/modify_node-to-labels_mapping_to_YARN)
     * [Configuration of Schedulers for node labels](#Configuration_of_Schedulers_for_node_labels)
 * [Specifying node label for application](#Specifying_node_label_for_application)
@@ -86,6 +87,13 @@ Notes:
     * If user don’t specify “(exclusive=…)”, exclusive will be ```true``` by default.
     * Run ```yarn cluster --list-node-labels``` to check added node labels are visible in the cluster.
 
+###Remove node labels from YARN
+
+* Remove cluster node labels:
+    * To remove one or more node labels, execute the following command: ```yarn rmadmin -removeFromClusterNodeLabels "<label>[,<label>,...]"```. The command argument should be a comma-separated list of node labels to remove.
+    * It is not allowed to remove a label which has been associated with queues, i.e., one or more queues have access to this label.
+    * To verify if specified node labels have been successfully removed, run ```yarn cluster --list-node-labels```.
+
 ###Add/modify node-to-labels mapping to YARN
 
 * Configuring nodes to labels mapping in **Centralized** NodeLabel setup