Two small tweaks to USB device mode chapter - mention "OTG"

in the title, and "USB gadget" in the description.

Reported by:	bcr@
Reviewed by:	bcr@ (earlier version)
Sponsored by:	The FreeBSD Foundation
Differential Revision:	https://reviews.freebsd.org/D15811

en_US.ISO8859-1/books/handbook/usb-device-mode/chapter.xml

@@ -9,7 +9,7 @@
   xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0"
   xml:id="usb-device-mode">
 
-  <title>USB Device Mode</title>
+  <title>USB Device Mode / USB OTG</title>
 
   <sect1 xml:id="usb-device-mode-synopsis">
     <title>Synopsis</title>
@@ -45,7 +45,8 @@
       including serial ports, network adapters, and mass storage,
       or a combination thereof.  A <acronym>USB</acronym> host like
       a laptop or desktop computer is able to access them just like
-      physical <acronym>USB</acronym> devices.</para>
+      physical <acronym>USB</acronym> devices.  Device mode is
+      sometimes called the <quote>USB gadget mode</quote>.</para>
 
     <para>There are two basic ways the hardware can provide the
       device mode functionality: with a separate "client port", which