As far as I can tell, comment shortcuts have been around since basically forever.
The [tour] link got added sometime soon before June 6, 2014 (officially confirmed on June 11†), a short while after our About page instead became a Tour, and references to it got renamed accordingly over the next few months. Before then, however, we used [about] to refer to the same page, so it's not so much a new link as a new name for an old link.
Like TuggyNE and Nitsua60 posted in comments there's a bunch of post shortcuts like this, including one to every Stack Exchange site (our shortcut is [rpg.se]).
† BESW reported this being implemented a whole week before the staff did. Upcoming, a new meta on whether BESW is a time traveler.