Explain dty/tty a bit and point to tty(4). Bump date.

Ok gdt@

share/man/man4/ucom.4

@@ -1,4 +1,4 @@
-.\" $NetBSD: ucom.4,v 1.25 2014/07/25 16:14:01 gdt Exp $
+.\" $NetBSD: ucom.4,v 1.26 2016/09/29 11:38:43 wiz Exp $
 .\"
 .\" Copyright (c) 1999 The NetBSD Foundation, Inc.
 .\" All rights reserved.
@@ -27,7 +27,7 @@
 .\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd July 25, 2014
+.Dd September 29, 2016
 .Dt UCOM 4
 .Os
 .Sh NAME
@@ -75,6 +75,11 @@ Note that while
 supports the (undocumented) pulse-per-second API normally used on
 conventional serial ports, USB serial devices typically have a varying
 latency around 1 ms due to the USB frame structure.
+.Pp
+The ttyXX devices are traditional dial-in devices; the dtyXX devices
+are used for dial-out.
+(See
+.Xr tty 4 . )
 .Sh FILES
 .Bl -tag -width Pa
 .It Pa /dev/dtyU?