Missing import on example/readline-demo/readline-demo.go

The demo `example/readline-demo/readline-demo.go` is missing the `os` module import, which is needed by the `listFiles` function (calls `os.ReadDir` on line 23) This one was simple ;) [bugfix-import.patch](https://github.com/user-attachments/files/23319194/bugfix-import.patch)