cloud labels can be added to an existing cluster (aws-samples#306)

* cloud labels can be added to an existing cluster

* changes as commented

Author: szuecs

ingress-controllers/readme.adoc

@@ -235,7 +235,13 @@ For this tutorial I assume you have GNU sed installed, if not read
 commands with `sed` to modify the files according to the `sed` command
 being run. If you are running BSD or MacOS you can use `gsed`.
 
-=== Create kops cluster with cloud labels
+We need to have cloud labels enabled for this ingress controller to work.
+You have 2 options, skip the section which does not fit in your case:
+
+1. <<Create a New Cluster>>
+2. <<Modify an Existing Cluster>>
+
+=== Create a New Cluster
 
 Cloud Labels are required to make Kube AWS Ingress Controller work,
 because it has to find the AWS Application Load Balancers it manages
@@ -250,13 +256,31 @@ your S3 Bucket name for kops configuration and you kops cluster name:
         export KOPS_CLUSTER_NAME=example.cluster.k8s.local
 
 
-The you create the kops cluster and validate that everything is set up properly.
-
+Then you create the kops cluster and validate that everything is set up properly.
 
         export KOPS_STATE_STORE=s3://${S3_BUCKET}
         kops create cluster --name $KOPS_CLUSTER_NAME --zones $AWS_AVAILABILITY_ZONES --cloud-labels kubernetes.io/cluster/$KOPS_CLUSTER_NAME=owned --yes
         kops validate cluster
 
+=== Modify an Existing Cluster
+
+To modify your existing kops cluster and update it.
+
+        export KOPS_STATE_STORE=s3://${S3_BUCKET}
+        kops edit cluster $KOPS_CLUSTER_NAME
+
+Add cloudLabels dependent on your $KOPS_CLUSTER_NAME, for example example.cluster.k8s.local:
+
+```
+ spec:
+   cloudLabels:
+     kubernetes.io/cluster/example.cluster.k8s.local: owned
+```
+
+Update the cluster with the new configuration:
+
+       kops update cluster $KOPS_CLUSTER_NAME --yes
+
 
 === IAM role