Add links to Workerman in README

Author: joanhey

frameworks/workerman/README.md

@@ -4,6 +4,11 @@ An asynchronous event driven PHP socket framework. Supports HTTP, Websocket, SSL
 
 All in pure PHP code.
 
+https://github.com/walkor/workerman
+https://manual.workerman.net/doc/en/
+https://www.workerman.net/
+
+
 ## Stack
 
 - **Language:** PHP