Add more detailed explanations about the tray app

ATxTray/README.md

@@ -2,4 +2,31 @@
 
 This project is a complement to the AutoTx *system service* that is running in
 the context of a logged-in user, delivering information and providing ways of
-interacting with the service from a GUI session.
+interacting with the service from a GUI session.
+
+## Tray Icon Colors
+
+The tray icon changes color depending on the state the service is currently in:
+
+- red background: service stopped
+- orange background: service running
+- black arrow: service idle
+- red arrow: service suspended due to system parameters
+- green arrow: transfer in progress
+
+## Tray Icon Context Menu
+
+More details on the service status is presented in the context menu of the tray
+icon (available on a right-click), including real-time information about the
+progress of a running transfer.
+
+In addition, the context menu offers a possibility for starting a new transfer
+by presenting the user with a folder selection dialog. This option is also
+available via a double-click on the tray icon directly.
+
+## Balloon Tooltips
+
+The tray app is designed to consume as little attention by the user as possible,
+the only situations where it actively signifies something are when a transfer is
+starting or has finished. A balloon tooltip will be shown for a short period,
+informing the user about the transfer.