Add an initial minimal description to the README

Author: marco-nicola

README.md

@@ -1 +1,9 @@
-# usbguard-simple-gui-py-qt
+# USBGuard Simple GUI Py/Qt
+
+A simple unambitious system tray applet and GUI for interacting with
+[USBGuard](https://usbguard.github.io/).
+
+It is implemented in Python 3, using 
+[Qt for Python / PySide2](https://www.qt.io/qt-for-python) for
+graphical interactions, and communicating with USBGuard via
+[D-Bus](https://dbus.freedesktop.org/doc/dbus-python/).