Question: We need to do some user documentation for a product we have been working on for the past few sprints. We are now starting a new project in the next sprint and the PO is making the documentation for the product produced previously a User story for this sprint.

I am just wondering your opinion on this approach. Personally, I don't agree that documentation is a User Story within Scrum because it doesn't produce any code. 

EDIT: Thanks for your opinions guys. I had it in the back of my head that a sprint was to implement an increment of working software, but your views have changed my outlook. Thank you for all your answers.

Answer: 
"As a user of X, I need to know how X works" seems like a legitimate user story to me. This could result in written documentation or online help.

The point isn't just code--it's meeting the users' requirements.
Ideally, documentation is part of every user story and never builds up. But, in the real world, that often doesn't happen. In that case, you should create a user story for catching up on a specific missing piece of documentation.

You're right, it doesn't produce any code. But it does satisfy a user requirement and should be prioritised against other user requirements.

If this means that it never gets done, because this and that functionality is being worked on then you probably didn't need the documentation that badly.