README.md: Add Hey to HarmonyOS in GUI Clients (#6244)

https://github.com/popsiclelmlm/Hey/blob/main/entry/src/main/cpp/README.md

---------

Co-authored-by: liumin01 <liumin01@roborock.com>

Author: popsiclelmlm

README.md

@@ -145,6 +145,8 @@
   - [v2rayN](https://github.com/2dust/v2rayN)
   - [GenyConnect](https://github.com/genyleap/GenyConnect)
   - [OneXray](https://github.com/OneXray/OneXray)
+- HarmonyOS
+  - [Hey](https://github.com/popsiclelmlm/Hey)
 
 ## Others that support VLESS, XTLS, REALITY, XUDP, PLUX...