Comic-book-movie diehards love their post-credits teaser scenes. But for Marvel’s Guardians of the Galaxy Vol. 2 (out May 5), there will be a special perk for more casual viewers who are willing to wait through the egregiously long credits scroll–that is, if they like pop music. Miley Cyrus, according to Guardians director James Gunn, has an uncredited voice role as Mainframe,…
