added tray menu

README.md

@@ -31,13 +31,41 @@ neither delivers keystrokes to the low-level hook nor accepts the layout change
 request, so the hotkey does nothing there. Reading the layout of a foreign window
 is not restricted, so the tooltip itself keeps working everywhere.
 
+## The tray
+
+The app works in the background and lives in the notification area. The settings
+window is a guest on the screen rather than the app itself: it shows up after the
+installation and whenever the icon or its menu is asked for. Both buttons in its
+title bar — minimise and close — put the window away into the tray and end nothing;
+the way out of the app is the Exit item of the tray menu.
+
+The window is hidden rather than closed. Closing it would take its handle with it,
+and everything hung on the window — the theme, the place it was left in, the
+computed layout — would have to be built anew on every show.
+
+The menu of the icon is a WPF one rather than a system one: that way it keeps to
+the theme and the language chosen in the settings, like the rest of the interface.
+
+Started by Windows itself, the app shows no window at all and goes straight to the
+tray — the user asked for it to be there when they sign in, not for a window to
+greet them every morning. The two builds tell such a launch apart differently: the
+registry entry of an unpacked build carries the `--startup` argument, while a
+package has no say in its command line, and Windows is asked about the activation
+instead.
+
+Should Windows refuse the icon — there is no notification area in a session without
+a desktop — the window takes its usual duties back: it shows up whatever the launch
+was, and closing it ends the app. The alternative would be an app the user can
+neither see nor quit.
+
 ## Startup
 
 Startup is switched on from the app's settings by whichever means the build has.
 A package declares it in the manifest as a `windows.startupTask`. A build unpacked
 into a folder registers itself the way desktop programs always have — under
 `HKCU\Software\Microsoft\Windows\CurrentVersion\Run`, which needs no administrator
-rights.
+rights. The command written there ends with `--startup`: that is how the app tells
+a launch of Windows' own doing from a launch by the user.
 
 Either way Windows lists the app in Settings — Apps — Startup; if the user turns
 it off there, the app can no longer turn it back on and says so instead of