added an example use of the onAdd prop
added an example use of the onAdd prop

moviepilot/react-mentions,effektif/react-mentions,rodrigues/react-mentions,rodrigues/react-mentions,younited/react-mentions,effektif/react-mentions,moviepilot/react-mentions,moviepilot/react-mentions,rodrigues/react-mentions,younited/react-mentions,pocketjoso/react-mentions,pocketjoso/react-mentions,younited/react-mentions,pocketjoso/react-mentions