timerfd_create.2: Add BUGS noting that timerfd supports fewer clock types than timer_create()

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>

man2/timerfd_create.2

@@ -508,6 +508,12 @@ main(int argc, char *argv[])
     exit(EXIT_SUCCESS);
 }
 .fi
+.SH BUGS
+Currently,
+.\" 2.6.29
+.BR timerfd_create ()
+supports fewer types of clock IDs than
+.BR timer_create (2).
 .SH "SEE ALSO"
 .BR eventfd (2),
 .BR poll (2),