Explain leases in kube-node-lease namespace doc

Add a reference to `Lease` resource api doc

Co-authored-by: Tim Bannister <[email protected]>

Author: rszsz

content/en/docs/concepts/overview/working-with-objects/namespaces.md

@@ -62,7 +62,10 @@ Kubernetes starts with four initial namespaces:
    * `default` The default namespace for objects with no other namespace
    * `kube-system` The namespace for objects created by the Kubernetes system
    * `kube-public` This namespace is created automatically and is readable by all users (including those not authenticated). This namespace is mostly reserved for cluster usage, in case that some resources should be visible and readable publicly throughout the whole cluster. The public aspect of this namespace is only a convention, not a requirement.
-   * `kube-node-lease` The namespace for lease objects associated with each node, which improves the performance of [heartbeats](/docs/concepts/architecture/nodes/#heartbeats) as the cluster scales.
+   * `kube-node-lease` This namespace holds [Lease](/docs/reference/kubernetes-api/cluster-resources/lease-v1/)
+      objects associated with each node. Node leases allow the kubelet to send
+      [heartbeats](/docs/concepts/architecture/nodes/#heartbeats) so that the control plane
+      can detect node failure.
 
 ### Setting the namespace for a request