modify PAPI_add_event() in the example. reformat some line.
modify PAPI_add_event() in the example. reformat some line.

arm-hpc/papi,arm-hpc/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,pyrovski/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,arm-hpc/papi,pyrovski/papi