Improve doc of /debug/api_priority_and_fairness/dump_requests

Include a non-phantom line.

Document the phantom lines (these are a bug, but not fixed yet, so
need to be documented).

Author: MikeSpreitzer

content/en/docs/concepts/cluster-administration/flow-control.md

@@ -409,18 +409,22 @@ When you enable the API Priority and Fairness feature, the kube-apiserver serves
   ```
   The output is similar to this:
   ```
-  PriorityLevelName, FlowSchemaName, QueueIndex, RequestIndexInQueue, FlowDistingsher, ArriveTime,
-  exempt,            <none>,         <none>,     <none>,              <none>,          <none>,
+  PriorityLevelName, FlowSchemaName, QueueIndex, RequestIndexInQueue, FlowDistingsher,       ArriveTime,
+  exempt,            <none>,         <none>,     <none>,              <none>,                <none>,
+  system,            system-nodes,   12,         0,                   system:node:127.0.0.1, 2020-07-23T15:26:57.179170694Z,
   ```
+  
+  In addition to the queued requests, the output includeas one phantom line for each priority level that is exempt from limitation.
 
   You can get a more detailed listing with a command like this:
   ```shell
   kubectl get --raw '/debug/api_priority_and_fairness/dump_requests?includeRequestDetails=1'
   ```
   The output is similar to this:
   ```
-  PriorityLevelName, FlowSchemaName, QueueIndex, RequestIndexInQueue, FlowDistingsher, ArriveTime, UserName, Verb,   APIPath, Namespace, Name,   APIVersion, Resource, SubResource,
-  exempt,            <none>,         <none>,     <none>,              <none>,          <none>,     <none>,   <none>, <none>,  <none>,    <none>, <none>,     <none>,   <none>,
+  PriorityLevelName, FlowSchemaName, QueueIndex, RequestIndexInQueue, FlowDistingsher,       ArriveTime,                     UserName,              Verb,   APIPath,                                                     Namespace, Name,   APIVersion, Resource, SubResource,
+  system,            system-nodes,   12,         0,                   system:node:127.0.0.1, 2020-07-23T15:31:03.583823404Z, system:node:127.0.0.1, create, /api/v1/namespaces/scaletest/configmaps,
+  system,            system-nodes,   12,         1,                   system:node:127.0.0.1, 2020-07-23T15:31:03.594555947Z, system:node:127.0.0.1, create, /api/v1/namespaces/scaletest/configmaps,
   ```
 
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