update docs, add kube-controller-manager flag which should not be set

Author: Rahul Sharma

docs/configuration/nodeipam.md

@@ -15,7 +15,10 @@ spec:
             - --cluster-cidr=10.192.0.0/10
 ```
 
-Once enabled, CCM will manage and allocate pod CIDRs to nodes. Make sure node IPAM allocation is disabled in kube-controller-manager to avoid both controllers competing to assign CIDRs to nodes.
+Once enabled, CCM will manage and allocate pod CIDRs to nodes.
+
+Note:
+Make sure node IPAM allocation is disabled in kube-controller-manager to avoid both controllers competing to assign CIDRs to nodes. To make sure its disabled, check and make sure kube-controller-manager is not started with `--allocate-node-cidrs` flag.
 
 ## Allocated subnet size
 By default, CCM allocates /24 subnet for ipv4 addresses and /64 for ipv6 addresses to nodes. If one wants different subnet range, it can be configured by using `--node-cidr-mask-size-ipv4` and `--node-cidr-mask-size-ipv6` flags.