GeneralPane: Add Hardcore Mode tooltip clarification

When Hardcore Mode is active, clarify in the Speed Limit tooltip that
values less than 100% won't slow emulation.

Source/Core/DolphinQt/Settings/GeneralPane.h

@@ -39,6 +39,7 @@ private:
   void LoadConfig();
   void OnSaveConfig();
   void OnEmulationStateChanged(Core::State state);
+  void UpdateDescriptionsUsingHardcoreStatus();
 
   // Widgets
   QVBoxLayout* m_main_layout;