Point to echo example on github as well for syntax highlighting

Author: nhooyr

README.md

@@ -33,7 +33,7 @@ go get nhooyr.io/websocket
 
 ## Examples
 
-For a production quality example that shows off the full API, see the [echo example on the godoc](https://godoc.org/nhooyr.io/websocket#example-package--Echo).
+For a production quality example that shows off the full API, see the [echo example on the godoc](https://godoc.org/nhooyr.io/websocket#example-package--Echo). On github, the example is at [example_echo_test.go](./example_echo_test.go).
 
 ### Server