Merge pull request openshift#8325 from andfasano/fix-add-node-cmd-docs

AGENT-863: docs fix

Author: openshift-merge-bot[bot]

docs/user/agent/add-node/add-nodes.md

@@ -2,7 +2,9 @@
 
 ## Pre-requisites
 1. The `oc` tool must be available in the execution environment (the "user host").
-2. The user host has a valid network connection to the target OpenShift cluster to be expanded.
+2. Ensure `oc` is properly configured to manage the cluster to be expanded, i.e. by either:
+   - running `oc login` command with the required cluster credentials, or
+   - running `export KUBECONFIG=<cluster `kubeconfig` file>`
 
 ## Setup
 1. Download the [node-joiner.sh](./node-joiner.sh) script in a working directory in
@@ -62,6 +64,7 @@ hosts:
       interfaces:
         - name: eth0
           macAddress: 00:02:46:e3:9e:9c
+```
 
 ## ISO generation
 Run the [node-joiner.sh](./node-joiner.sh):