Minerva, ChichesterRakie Ayola is superb in a story about the exploitation of a Black female playwright by the great and the greedy of London's theatreland It's quite a title. Adrienne Kennedy " now a belatedly revered American playwright " impulsively came to London in 1966, young son in tow. She met John Lennon and sort of premiered a play at Laurence Olivier's National Theatre. A fairytale becomes a devastating s…