I've asked myself this question too.
My first thought was that it would be located at the back, though, on the images it can't be found there either.
So yes, it seems to be an error in the documentation.
I wonder if there will be an internal psu available for the css, though I doubt it. Just as with the 2011-RM, it still confuses me why they add those possibilities and then let users craft their own internal psu's.