Add information about topologySpeadConstraint duplicate values

content/en/docs/concepts/scheduling-eviction/topology-spread-constraints.md

@@ -70,6 +70,10 @@ spec:
   ### other Pod fields go here
 ```
 
+{{< note >}}
+There can only be one topologySpreadConstraint for a given topologyKey and whenUnsatisfiable value. For example, if you have defined a topologySpreadConstraint that uses the topologyKey "kubernetes.io/hostname" and whenUnsatisfiable value "DoNotSchedule", you can only add another topologySpreadConstraint for the topologyKey "kubernetes.io/hostname" if you use a different whenUnsatisfiable value.
+{{< /note >}}
+
 You can read more about this field by running `kubectl explain Pod.spec.topologySpreadConstraints` or
 refer to the [scheduling](/docs/reference/kubernetes-api/workload-resources/pod-v1/#scheduling) section of the API reference for Pod.