Michelle Obama’s book tour promoting her upcoming memoir, “Becoming,” was expected to be big — the former first lady has sold out arenas, after all. And now we know just how star-studded it will be. Obama on Tuesday announced an eclectic slate of famous folks who will be joining her onstage during her stops at various cities. The list includes media queen Oprah Winfrey, “Blackish” actress Tracee Ellis Ross, former White House adviser Valerie Jarrett, actresses Reese Witherspoon and Sarah Jessica Parker, comedian Phoebe Robinson, former NPR host Michelle Norris and poet Elizabeth Alexander.