##### Does this button stay here even after they have watched the tour?

Just like the CP > Build > Layout link, the "Take a tour" link remains after they've finished, and they can take the tour as many times as they want without reloading the page.

##### Is this for new sites or for all users?

It's designed for anyone without expert OS knowlowedge. Currently, the link shows up for all admins in the help region when they view the home page. The purpose of this PR is to get feedback on the tour. I don't think it's been decided exactly when and how the tour will show up.