Attaching to the init process returns EINVAL,

so give an example that is more likely to work.
Stolen from the ktrace(1) manual page.

PR:		128222
Submitted by:	Mateusz Guzik <mjguzik@gmail.com>

usr.bin/truss/truss.1

@@ -1,6 +1,6 @@
 .\" $FreeBSD$
 .\"
-.Dd January 2, 2004
+.Dd January 22, 2009
 .Dt TRUSS 1
 .Os
 .Sh NAME
@@ -85,7 +85,7 @@ options are mutually exclusive.)
 # Do the same, but put the output into a file
 .Dl $ truss -o /tmp/truss.out /bin/echo hello
 # Follow an already-running process
-.Dl $ truss -p 1
+.Dl $ truss -p 34
 .Sh SEE ALSO
 .Xr kdump 1 ,
 .Xr ktrace 1 ,