Update README.md (Sapd#276) with third party library

Link to gnome-shell-extension-HeadsetControl

Author: ChrisLauinger77

README.md

@@ -183,6 +183,8 @@ The following additional software can be used to enable control via a GUI
 
 [headset-charge-indicator](https://github.com/centic9/headset-charge-indicator/) adds a system tray icon, displaying the current amount of battery. Also provides controls via the icon's menu (Python based)
 
+[gnome-shell-extension-HeadsetControl](https://github.com/ChrisLauinger77/gnome-shell-extension-HeadsetControl/) adds a system tray icon, displaying the current amount of battery. Also provides controls via the icon's menu (gnome-shell 42 and later)
+
 #### Windows
 
 [HeadsetControl-SystemTray](https://github.com/zampierilucas/HeadsetControl-SystemTray) adds a system tray icon, displaying the current amount of battery. (Python based)