How can I add a shortcut to another Google Drive folder?

A friend of mine has a couple of documents in a Google Drive folder (let's say X).

And I have the rest of the files in another folder, let's say Y.

How can I add a link inside Y so that folder X is visible inside? In other words I'm trying to achieve this:

-- Folder Y:    |-- folder Y files    |-- Folder X (which is owned by another Drive user)          |-- Folder X files should show up here

There seems to be no option to add a link to another drive.