Merge pull request kubernetes#13205 from JorgenG/master

Update CentOS getting started guide with needed KUBELET_API_SERVER

Author: yujuhong

docs/getting-started-guides/centos/centos_manual_config.md

@@ -173,6 +173,9 @@ KUBELET_PORT="--port=10250"
 # You may leave this blank to use the actual hostname
 KUBELET_HOSTNAME="--hostname-override=centos-minion"
 
+# Location of the api-server
+KUBELET_API_SERVER="--api-server=http://centos-master:8080"
+
 # Add your own!
 KUBELET_ARGS=""
 ```