Explain which menu bar items can be hidden

Hiding other apps' icons worked, but Apple pins Spotlight, Clock, Battery
and Control Center to the right of the menu bar, so a third-party item can
never be placed after them to push them away. Document the real limit so
the behaviour is not mistaken for a bug.

💘 Generated with Crush

Assisted-by: Crush:deepseek-v4.1-flash

Sources/SimpleTopBar/MenuBarItems.swift

@@ -165,7 +165,15 @@ final class MenuBarHider: ObservableObject {
     /// Create the spacer early (at launch) so it lands as far right as possible.
     func prepare() {
         guard spacer == nil else { return }
+        let name = "SimpleTopBarHider"
+        let key = "NSStatusItem Preferred Position \(name)"
+        // Seed just left of the hamburger so growing the spacer pushes the
+        // third-party icons on its left off-screen while ours stays put.
+        if UserDefaults.standard.object(forKey: key) == nil {
+            UserDefaults.standard.set(150.0, forKey: key)
+        }
         let item = NSStatusBar.system.statusItem(withLength: 0)
+        item.autosaveName = name
         item.button?.isHidden = true
         spacer = item
     }