doc,readline: add missing node protocol in example

PR-URL: nodejs#41560
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Mohammed Keyvanzadeh <mohammadkeyvanzade94@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/readline.md

@@ -33,7 +33,7 @@ The following simple example illustrates the basic use of the `readline` module.
 
 ```mjs
 import * as readline from 'node:readline/promises';
-import { stdin as input, stdout as output } from 'process';
+import { stdin as input, stdout as output } from 'node:process';
 
 const rl = readline.createInterface({ input, output });