diff --git a/README.md b/README.md
index 967b6c3..fe25249 100644
--- a/README.md
+++ b/README.md
@@ -14,3 +14,4 @@ By default, hbbs listens on 21115(tcp) and 21116(tcp/udp), hbbr listens on 21117
 
 For sustainable development, this software is no longer available for free. Please pay USD $99 to my paypal **info@rustdesk.com**. Then send email to info@rustdesk.com to confirm the payment, and I will reply you with the program.
 
+> You can write your own rustdesk-server, the protocol is [open sourced](https://github.com/rustdesk/rustdesk/tree/master/src/rendezvous_mediator.rs). You just need some time to understand, instead you can buy me a cup of tea, **:)**