doc: clarify changes in readableFlowing

PR-URL: #45554
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Daeyeon Jeong <daeyeon.dev@gmail.com>
Reviewed-By: Yagiz Nizipli <yagiz@nizipli.com>

Author: cola119

doc/api/stream.md

@@ -880,8 +880,10 @@ pass.unpipe(writable);
 // readableFlowing is now false.
 
 pass.on('data', (chunk) => { console.log(chunk.toString()); });
+// readableFlowing is still false.
 pass.write('ok');  // Will not emit 'data'.
 pass.resume();     // Must be called to make stream emit 'data'.
+// readableFlowing is now true.
 ```
 
 While `readable.readableFlowing` is `false`, data may be accumulating