client-go workqueue: clarify parallel reenqueuing

"Is allowed" does not exactly say what happens. Let's be more explicit.

staging/src/k8s.io/client-go/util/workqueue/doc.go

@@ -22,5 +22,6 @@ limitations under the License.
 //     will only be processed once.
 //   - Multiple consumers and producers. In particular, it is allowed for an
 //     item to be reenqueued while it is being processed.
+//     In this case it will be processed again.
 //   - Shutdown notifications.
 package workqueue