add HISTORY to ldap.1

Ok?

Index: ldap.1
===================================================================
RCS file: /cvs/src/usr.bin/ldap/ldap.1,v
retrieving revision 1.7
diff -u -p -r1.7 ldap.1
--- ldap.1 3 Jul 2018 10:10:09 -0000 1.7
+++ ldap.1 3 Jul 2018 19:19:21 -0000
@@ -233,6 +233,11 @@ Match Group ldapusers
.%R RFC 4516
.%T Lightweight Directory Access Protocol (LDAP): Uniform Resource Locator
.Re
+.Sh HISTORY
+The
+.Nm
+program first appeared in
+.Ox 6.4 .
.Sh AUTHORS
.An -nosplit
The