Bucky Barnes is the White Wolf, the star of a tie-in comic
The post-credits scene, after the lengthy list of visual effects artists, features Shuri dismissing some Wakandan youth from a hut where they were with the "White Wolf." Hinted at earlier in the film when Shuri tells T'Challa he's "brought her another white boy to fix" (emphasis ours). The White Wolf that they refer to is Bucky Barnes, robed in blue and red. Shuri lets Bucky know it's time for the next step, and we're out on: "Black Panther will return in Avengers: Infinity War."
If you stuck around for the credits on Captain America: Civil War, you know an armless Bucky was placed into stasis in Wakanda as Steve Rogers, free of the Captain America title and shield went off to... hey! Why wasn't Cap in this movie? What did Shuri do to Bucky? Believe it or not, the answers lie in a tie-in comic to Avengers: Infinity War, released at the end of January. Marvel's Avengers: Infinity War Prelude #1 explains that Shuri created a "cyber-mind," or a digital copy of Bucky's mind to concoct an algorithm that would rewrite real Bucky's brain to free him of the code-word control that was such a problem in Civil War; Steve Rogers, Falcon, and Black Widow are off saving the world like undercover Avengers, stopping people dealing in stolen Chitauri weapons; Tony Stark is making new armor; Hawkeye has retired and is with his family; and Vision and Scarlet Witch have moved in together in Europe. There will be a second prelude comic released at the end of February that is going to include Doctor Strange and Thor, further priming the comic book audience for May's film with information that probably should have been in one of the movies? Maybe?