doc: add unref for input in readline

Author: AnupamaP

doc/api/readline.md

@@ -628,6 +628,12 @@ the best compatibility if it defines an `output.columns` property and emits
 a `'resize'` event on the `output` if or when the columns ever change
 ([`process.stdout`][] does this automatically when it is a TTY).
 
+In order to end the wait for the `stdin` input stream (so that the program does not appear to have hanged), `unref` function can be used:
+
+```js
+process.stdin.unref();
+```
+
 ### Use of the `completer` function
 
 The `completer` function takes the current line entered by the user