Say the remedy beside the problem in status

A status that names what is wrong and not what to do about it makes somebody go
and find the command — and the command is the whole point of having noticed.
The hint existed on one of the two paths that print this.

cmd/mesh-control/main.go

@@ -1880,6 +1880,10 @@ func statusCommand(ctx context.Context, args []string) error {
 				fmt.Printf("  %-18s assigned to nothing\n", "")
 			}
 		}
+		// The remedy, beside the problem. A status that says what is wrong and not what to do
+		// about it makes somebody go and find the command, and the command is the whole point of
+		// having noticed.
+		fmt.Printf("\n  `build --behind` builds them; `push --behind` sends them on\n")
 		fmt.Println()
 	}