With its rich store of “behind the music’’ anecdotes and intimate snapshots of legends like John Lennon and Paul McCartney, Aretha Franklin, Joni Mitchell, and James Taylor, Carole King’s memoir “Natural Woman’’ is required reading for rock fans. For a broader audience, “Natural Woman’’ presents an engrossing and affecting memoir of a hugely gifted artist whom fame, fortune, and acclaim could not deter from undertaking the most harrowing journey into the backwoods of her own soul.