tzcode: Document zic's -D option.

Sponsored by:	Klara, Inc.
Reviewed by:	allanjude
Differential Revision:	https://reviews.freebsd.org/D38141

contrib/tzcode/zic.8

@@ -3,7 +3,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd December 15, 2022
+.Dd January 21, 2023
 .Dt ZIC 8
 .Os
 .Sh NAME
@@ -71,6 +71,8 @@ mishandles timestamps after the year 2038 anyway.
 Also see the
 .Fl r
 option for another way to alter output size.
+.It Fl D
+Do not create directories.
 .It Fl d Ar directory
 Create time conversion information files in the named directory rather than
 in the standard directory named below.