[FLINK-20664][k8s][doc] Update RBAC section in native kubernetes document

This closes #14447

docs/deployment/resource-providers/native_kubernetes.md

@@ -307,7 +307,8 @@ $ kubectl create clusterrolebinding flink-role-binding-default --clusterrole=edi
 {% endhighlight %}
 
 If you do not want to use the `default` service account, use the following command to create a new `flink-service-account` service account and set the role binding.
-Then use the config option `-Dkubernetes.jobmanager.service-account=flink-service-account` to make the JobManager pod use the `flink-service-account` service account to create and delete TaskManager pods.
+Then use the config option `-Dkubernetes.service-account=flink-service-account` to make the JobManager pod use the `flink-service-account` service account to create/delete TaskManager pods and leader ConfigMaps. 
+Also this will allow the TaskManager to watch leader ConfigMaps to retrieve the address of JobManager and ResourceManager.
 
 {% highlight bash %}
 $ kubectl create serviceaccount flink-service-account

docs/deployment/resource-providers/native_kubernetes.zh.md

@@ -307,7 +307,8 @@ $ kubectl create clusterrolebinding flink-role-binding-default --clusterrole=edi
 {% endhighlight %}
 
 If you do not want to use the `default` service account, use the following command to create a new `flink-service-account` service account and set the role binding.
-Then use the config option `-Dkubernetes.jobmanager.service-account=flink-service-account` to make the JobManager pod use the `flink-service-account` service account to create and delete TaskManager pods.
+Then use the config option `-Dkubernetes.service-account=flink-service-account` to make the JobManager pod use the `flink-service-account` service account to create/delete TaskManager pods and leader ConfigMaps. 
+Also this will allow the TaskManager to watch leader ConfigMaps to retrieve the address of JobManager and ResourceManager.
 
 {% highlight bash %}
 $ kubectl create serviceaccount flink-service-account