kubernetes#2501 add documented

Author: LiuQhahah

docs/metrics/cluster/node-metrics.md

@@ -14,3 +14,5 @@
 | kube_node_status_condition   | Gauge       | The condition of a cluster node                                                                                           |                                                                                                                                                                                          | `node`=&lt;node-address&gt; <br> `condition`=&lt;node-condition&gt; <br> `status`=&lt;true\|false\|unknown&gt;                                                                                                                                                                                                                                                                                                                                            | STABLE       |
 | kube_node_created            | Gauge       | Unix creation timestamp                                                                                                   | seconds                                                                                                                                                                                  | `node`=&lt;node-address&gt;                                                                                                                                                                                                                                                                                                                                                                                                                               | STABLE       |
 | kube_node_deletion_timestamp | Gauge       | Unix deletion timestamp                                                                                                   | seconds                                                                                                                                                                                  | `node`=&lt;node-address&gt;                                                                                                                                                                                                                                                                                                                                                                                                                               | EXPERIMENTAL |
+| kube_node_volumes_in_use_count | Gauge       | Number of volumes in use on the node                                                                                                |                                                                                                                                                                                   | `node`=&lt;node-address&gt;                                                                                                                                                                                                                                                                                                                                                                                                                               | STABLE |
+| kube_node_volumes_attached_count | Gauge       | Number of volumes attached to the node                                                                                                   |                                                                                                                                                                                   | `node`=&lt;node-address&gt;                                                                                                                                                                                                                                                                                                                                                                                                                               | STABLE |