The talent is located in the Brewmaster spec tree on the right, 2nd to last (bottom) row.
It states: Blackout Kick also empowered your next ability:
Celestial Brew: Gain up to 3 additional stacks of Purified Chi.
EDIT: I see it now: “Increases the absorption of your next Celestial Brew by 60%.” But it still doesn’t make sense to me because this buff only lasts 14 seconds and Celestial Brew has a 36 second cooldown. You have to USE Celestial Brew FIRST to even get the buff, but once you do that, you don’t seem to be able to USE the buff. ???