notify(2) should really mention postnote(2)

Reference: /n/sources/patch/applied/notify-manpage
Date: Sat Apr 23 18:39:15 CES 2011
Signed-off-by: aiju@phicode.de

--- /sys/man/2/notify	Sat Apr 23 18:39:02 2011
+++ /sys/man/2/notify	Sat Apr 23 18:38:59 2011
@@ -233,6 +233,7 @@
 .br
 .B /sys/src/libc/port/atnotify.c
 .SH SEE ALSO
+.IR postnote (2),
 .IR intro (2),
 .I notejmp
 in