Shania Twain is heading to The Voice to advise season 12’s top 12 contestants starting April 24 on NBC. Previous key advisors on the show have been Garth Brooks, Tim McGraw, Faith Hill, Taylor Swift, Miley Cyrus, Rihanna, Nate Ruess and Coldplay’s Chris Martin. Excited to announce that I’ll appear on @nbcthevoice this month, as…