update doc (easegress-io#705)

doc/reference/wasmhost.md

@@ -86,11 +86,10 @@ And then create the pipeline `wasm-pipeline` which includes a `WasmHost` filter:
 ```bash
 $ echo '
 name: wasm-pipeline
-kind: HTTPPipeline
+kind: Pipeline
 flow:
  - filter: wasm
  - filter: proxy
- jumpIf: { fallback: END }
 
 filters:
  - name: wasm
@@ -100,17 +99,20 @@ filters:
  timeout: 100ms
  - name: proxy
  kind: Proxy
- mainPool:
-   servers:
+ pools:
+ - servers:
  - url: http:https://127.0.0.1:9095
  loadBalance:
  policy: roundRobin' | egctl object create
 ```
 
 Note we are using the path of the Wasm file as the value of `code` in the spec of `WasmHost`, but the value of `code` can also be a URL (HTTP/HTTPS) or the base64 encoded Wasm code.
 
-Then, we need to set up the backend service by following [the steps in README.md](../README.md#test).
+Then, we need to set up the backend service by following command.
 
+```bash
+go run easegress/example/backend-service/echo/echo.go
+```
 ## Test
 
 Now, let's send some requests to the HTTP server, we can see request header and body are set as desired.