getdelim.3: Add a missing Vt

[Josiah Frentsos]

Index: getdelim.3
===================================================================
RCS file: /cvs/src/lib/libc/stdio/getdelim.3,v
retrieving revision 1.6
diff -u -p -r1.6 getdelim.3
--- getdelim.3  17 Oct 2017 22:47:58 -0000      1.6
+++ getdelim.3  20 Dec 2022 17:45:54 -0000
@@ -57,7 +57,8 @@ The buffer is
 and includes the delimiter.
 The
 .Fa delimiter
-character must be representable as an unsigned char.
+character must be representable as an
+.Vt unsigned char .
 .Pp
 If
 .Fa *n