docs: update notification body message when a new Cassiopee version is available

Refs #640

main.js

@@ -135,7 +135,7 @@ const lookForUpdates = function() {
                             }
                             let notif = new Notification({
                                 title: `Cassiopee version ${data.latest} is available`,
-                                body: `Click to download update installer`,
+                                body: `The desktop distribution of Cassiopeia will no longer be updated in 2024. You are invited to use the progressive web app Cassiopée instead. Click to download update installer.`,
                                 icon: nativeImage.createFromPath(iconPath) // @see https://github.com/electron/electron/issues/24221
                             });
                             notif.addListener("click", () => {