feat: Update notifications: a notification and tray icon when there's a new Steamify

ui/qml/Texts.qml

@@ -21,6 +21,9 @@ QtObject {
         launcher: { label: "Steamify shortcut", hint: "The app on the desktop and in the launcher",
                     body: "Opens the newest Steamify app, so you never need the install command again. Steamify Terminal in the launcher opens the terminal menu.",
                     changes: ["Steamify CachyOS on the desktop and in the launcher (the app)", "Steamify Terminal in the launcher"] },
+        notify: { label: "Update notifications", hint: "A notification when there's a new Steamify",
+                  body: "Checks once a day and when you log in to the desktop. When there's a new Steamify you get a notification and a tray icon: open the app to see what's new and choose what to update, or skip that version. It never updates anything by itself.",
+                  changes: ["A daily check (systemd user timer), only on the desktop", "Tray icon only while an update is waiting", "Skip this version: quiet until the next one"] },
         vram: { label: "VRAM booster", hint: "The game in front keeps its VRAM",
                 body: "Like SteamOS 3.9: the game you're playing keeps its video memory, and background apps are moved out first. Without it a game that needs most of the video memory can spill into system RAM and stutter. Shown for GPUs whose driver supports it (AMD, Intel) on kernel 7.2 or newer.",
                 changes: ["dmemcg-booster (system and user service)", "plasma-foreground-booster, which tells it which window is in front", "Off: removed again, unless you had installed them yourself"] },