Add elksmart-comm for transceiving infrared codes

The receive functionality is quite unstable,
however useful enough for something that is officially unsupported.

The gadget is picky about cables,
but it has ridiculous reach when it works.

README.adoc

@@ -27,6 +27,8 @@ to other people as well:
    pseudo-random data; it should be fast enough to saturate most devices
  - 'big-brother' tracks the title of the active window and the idle state of
    the user and writes these events to standard output.
+ - 'elksmart-comm' interfaces with ELK Smart infrared dongles,
+   partially reimplementing the Ocrustar mobile app.
 
 Few of them are useful outside of Linux.
 
@@ -37,7 +39,9 @@ Regular releases are sporadic.  git master should be stable enough.
 Building
 --------
 Build dependencies: CMake, pkg-config, liberty (included) +
-Runtime dependencies: libpulse, libx11, dbus-1, libgdm (optional)
+Runtime dependencies: libpulse, libx11, dbus-1 +
+Optional runtime dependencies:
+libusb-1.0 (elksmart-comm), libgdm (gdm-switch-user)
 
  $ git clone --recursive https://git.janouch.name/p/desktop-tools.git
  $ mkdir desktop-tools/build