Rephrase doc about Deployment .spec.rollbackTo field

docs/concepts/workloads/controllers/deployment.md

@@ -866,13 +866,20 @@ a Pod is considered ready, see [Container Probes](/docs/concepts/workloads/pods/
 
 ### Rollback To
 
-`.spec.rollbackTo` is an optional field with the configuration the Deployment is rolling back to. Setting
-this field will trigger a rollback, and this field will be cleared every time a rollback is done.
+`.spec.rollbackTo` is an optional field with the configuration the Deployment
+should roll back to. Setting this field triggers a rollback, and this field will
+be cleared by the server after a rollback is done.
+
+Because this field will be cleared by the server, it should not be used
+declaratively. For example, you should not perform `kubectl apply` with a
+manifest with `.spec.rollbackTo` field set.
 
 #### Revision
 
-`.spec.rollbackTo.revision` is an optional field specifying the revision to rollback to. This defaults
-to 0, meaning rollback to the last revision in history.
+`.spec.rollbackTo.revision` is an optional field specifying the revision to roll
+back to. Setting to 0 means rolling back to the last revision in history;
+otherwise, means rolling back to the specified revision. This defaults to 0 when
+[`spec.rollbackTo`](#rollback-to) is set.
 
 ### Revision History Limit