HUMPHREY NJOKU Chioma Ajunwa had no idea just how important her victory in the Summer Olympics of 1996 was - until Nigeria announced a three-day national holiday in her honour. Ajunwa explains just what it meant to be the first black African woman to win Olympic gold in a field event - and how she didn't understand the significance until she was swamped by a crowd that included dance troupes on a stopover in Senegal, on the way home. "I am proof anyone can rise to the top, irrespective of background," said Nigeria’s first and only individual Olympic goal medalist, in…