**Is your feature request related to a problem? Please describe.**

MenuItem labels are meant to be short. There's currently no place to elaborate/clarify them.

**Describe the solution you'd like**

`NSMenuItem` supports a [`toolTip`](https://developer.apple.com/documentation/appkit/nsmenuitem/1514848-tooltip?language=objc) property. Would be nice if Electron could expose this.

From what I could find, [GTK (Linux) does not have any way to set tooltip on menu items](https://developer.gnome.org/gtk3/stable/GtkMenuItem.html).

No idea about Windows.

**Describe alternatives you've considered**

None.

**Additional context**

No.
shell/browser/ui/atom_menu_model.h
virtual void OnMenuWillShow() {}
    
    virtual void OnMenuWillClose() {}
  };
  explicit AtomMenuModel(Delegate* delegate);
  ~AtomMenuModel() override;
  void AddObserver(Observer* obs) { observers_.AddObserver(obs); }
  void RemoveObserver(Observer* obs) { observers_.RemoveObserver(obs); }
  void SetRole(int index, const base::string16& role);
  base::string16 GetRoleAt(int index);
  bool GetAcceleratorAtWithParams(int index,
                                  bool use_default_accelerator,
                                  ui::Accelerator* accelerator) const;
  bool ShouldRegisterAcceleratorAt(int index) const;
  bool WorksWhenHiddenAt(int index) const;
  
  void MenuWillClose() override;
  void MenuWillShow() override;
  using SimpleMenuModel::GetSubmenuModelAt;
  AtomMenuModel* GetSubmenuModelAt(int index);
 private:
  Delegate* delegate_;  
  std::map<int, base::string16> roles_;  
  base::ObserverList<Observer> observers_;
  DISALLOW_COPY_AND_ASSIGN(AtomMenuModel);
};
}  
#endif