Make it clear what the userland traces are in the ktrace(1) man page.

MFC after:	2 weeks

usr.bin/ktrace/ktrace.1

@@ -28,7 +28,7 @@
 .\"	@(#)ktrace.1	8.1 (Berkeley) 6/6/93
 .\" $FreeBSD$
 .\"
-.Dd July 24, 2017
+.Dd August 26, 2019
 .Dt KTRACE 1
 .Os
 .Sh NAME
@@ -130,7 +130,8 @@ trace signal processing
 .It Cm t
 trace various structures
 .It Cm u
-userland traces
+userland traces generated by
+.Xr utrace 2
 .It Cm w
 context switches
 .It Cm y
@@ -184,7 +185,8 @@ Disable tracing of all user-owned processes:
 .Xr dtrace 1 ,
 .Xr kdump 1 ,
 .Xr truss 1 ,
-.Xr ktrace 2
+.Xr ktrace 2 ,
+.Xr utrace 2
 .Sh HISTORY
 The
 .Nm