Document that cal(1) cannot start a week with Monday.

Reviewed by:	bcr
Approved by:	bcr (doc)
Approved by:	krion (mentor, implicit), mat (mentor, implicit)
Differential Revision:	https://reviews.freebsd.org/D19491

usr.bin/ncal/ncal.1

@@ -24,7 +24,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd June 08, 2018
+.Dd March 7, 2019
 .Dt CAL 1
 .Os
 .Sh NAME
@@ -199,3 +199,12 @@ codes is historically naive for many countries.
 .Pp
 Not all options are compatible and using them in different orders
 will give varying results.
+.Pp
+It is not possible to display Monday as the first day of the week with
+.Nm cal .
+If you want to use
+.Nm cal
+and want to have Mondays to start the week, use the ports version
+.Pq Pa deskutils/cal
+rather than the base system
+.Nm cal .