Help: Add shortcut to "Go to Help Mode" button tool tip

Change-Id: Iee56afd5dd78e1e105acffc06d4a0931b0cca036
Reviewed-by: Karsten Heimrich <karsten.heimrich@digia.com>

src/plugins/help/helpwidget.h

@@ -72,8 +72,10 @@ private slots:
     void updateForwardMenu();
     void updateWindowTitle();
     void helpModeButtonClicked();
+    void updateHelpModeButtonToolTip();
 
 private:
+    QAction *m_switchToHelp;
     QMenu *m_backMenu;
     QMenu *m_forwardMenu;
     QAction *m_openHelpMode;