why does google want link to mobile site on desktop site 2013

this article</a> the author says that...



"When using alternative URLs for mobile, Google would like... use of the link alternate tag on desktop pages pointing to the mobile version of the URL."



if i understand correctly, they're saying that i should put a link on my desktop site to the mobile site. is that correct? if so, why would they want that? if its not correct, what are they trying to say that i'm not understanding?



please advise. thanks in advance!</div>