doc: update broken link (#1945)

README.md

@@ -53,7 +53,7 @@ A/B testing, canary release, blue-green deployment, limit rate, defense against
     - [TCP/UDP Proxy](doc/stream-proxy.md): Dynamic TCP/UDP proxy.
     - [Dynamic MQTT Proxy](doc/plugins/mqtt-proxy.md): Supports to load balance MQTT by `client_id`, both support MQTT [3.1.*](http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html), [5.0](https://docs.oasis-open.org/mqtt/mqtt/v5.0/mqtt-v5.0.html).
     - [gRPC proxy](doc/grpc-proxy.md): Proxying gRPC traffic.
-    - [gRPC transcoding](doc/plugins/grpc-transcoding.md): Supports protocol transcoding so that clients can access your gRPC API by using HTTP/JSON.
+    - [gRPC transcoding](doc/plugins/grpc-transcode.md): Supports protocol transcoding so that clients can access your gRPC API by using HTTP/JSON.
     - Proxy Websocket
     - Proxy Protocol
     - Proxy Dubbo: Dubbo Proxy based on Tengine.