Add ToC and fix markdown formatting in cluster management doc.

docs/admin/cluster-management.md

@@ -1,6 +1,9 @@
 ---
 ---
 
+* TOC
+{:toc}
+
 This document describes several topics related to the lifecycle of a cluster: creating a new cluster,
 upgrading your cluster's
 master and worker nodes, performing node maintenance (e.g. kernel upgrades), and upgrading the Kubernetes API version of a
@@ -102,6 +105,7 @@ On GKE you configure cluster autoscaler either on cluster creation or update or
 to the corresponding `gcloud` commands.
 
 Examples:
+
 ```shell
 gcloud container clusters create mytestcluster --zone=us-central1-b --enable-autoscaling=true --min-nodes=3 --max-nodes=10 --num-nodes=5
 ```