add open NodeJs to readme examples

Author: zth

README.md

@@ -46,6 +46,8 @@ Help all ReScript Node.js apps and libraries to be built faster by reducing the
 ### Stream a file into stdout:
 
 ```rescript
+open NodeJs
+
 Fs.createReadStream("/path")
   ->Stream.pipe(Process.(stdout(process)))
   ->Stream.onError(_ => Js.log("handleError"))
@@ -54,6 +56,8 @@ Fs.createReadStream("/path")
 ### Echo server:
 
 ```rescript
+open NodeJs
+
 Http.createServer((request, response) => {
   request->Stream.onData(data => Js.log(data))
   request->Stream.pipe(response)->ignore