m4(1): Add a SEE ALSO section and reference an AT&T manual

Obtained from:	OpenBSD
MFC after:	1 week

usr.bin/m4/m4.1

@@ -33,7 +33,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd $Mdocdate: June 15 2017 $
+.Dd April 8, 2021
 .Dt M4 1
 .Os
 .Sh NAME
@@ -455,6 +455,17 @@ But note that the
 macro can modify the exit status, as can the
 .Fl E
 flag.
+.Sh SEE ALSO
+.Rs
+.\" 4.4BSD PSD:17
+.%A B. W. Kernighan
+.%A D. M. Ritchie
+.%I AT&T Bell Laboratories
+.%T The M4 Macro Processor
+.%R Computing Science Technical Report
+.%N 59
+.%D July 1977
+.Re
 .Sh STANDARDS
 The
 .Nm