doc: Expound on inputattach service.

* doc/guix.texi (Miscellaneous Services): Expound documentation of
inputattach service.

doc/guix.texi

@@ -22506,19 +22506,31 @@ resolution when the graphical console window resizes.
 @cindex inputattach
 @subsubheading inputattach Service
 
-@deftp {Data Type} inputattach-configuration
-@table @asis
-@item @code{device-type} The type of device to connect to.
-@item @code{device} The device file to connect to the device.
-@item @code{log-file} The file to log messages to.
-@end table
-@end deftp
+@cindex tablet input, for Xorg
+@cindex touchscreen input, for Xorg
+The @uref{https://linuxwacom.github.io/, inputattach} service allows you to
+use input devices such as Wacom tablets, touchscreens, or joysticks with the
+Xorg display server.
 
-@deffn {Scheme Procedure} inputattach-service-type
-Return a service that runs inputattach on a device and
+@deffn {Scheme Variable} inputattach-service-type
+Type of a service that runs @command{inputattach} on a device and
 dispatches events from it.
 @end deffn
 
+@deftp {Data Type} inputattach-configuration
+@table @asis
+@item @code{device-type} (default: @code{"wacom"})
+The type of device to connect to.  Run @command{inputattach --help}, from the
+@code{inputattach} package, to see the list of supported device types.
+
+@item @code{device} (default: @code{"/dev/ttyS0"})
+The device file to connect to the device.
+
+@item @code{log-file} (default: @code{#f})
+If true, this must be the name of a file to log messages to.
+@end table
+@end deftp
+
 @subsection Dictionary Services
 @cindex dictionary
 The @code{(gnu services dict)} module provides the following service: