Fix benchmark usage, add instructions

[Tyriar]

Commenting out #5645 optimization:

   Context "out-test/benchmark/Event.benchmark.js"
      Context "Emitter.fire()"
         Context "0 listeners"
            Case "#1" : 5 runs - average runtime: 5.62 ms
         Context "1 listener"
            Case "#1" : 5 runs - average runtime: 17.27 ms
         Context "2 listeners"
            Case "#1" : 5 runs - average runtime: 26.54 ms
         Context "5 listeners"
            Case "#1" : 5 runs - average runtime: 57.61 ms

main:

   Context "out-test/benchmark/Event.benchmark.js"
      Context "Emitter.fire()"
         Context "0 listeners"
            Case "#1" : 5 runs - average runtime: 2.06 ms
         Context "1 listener"
            Case "#1" : 5 runs - average runtime: 9.72 ms
         Context "2 listeners"
            Case "#1" : 5 runs - average runtime: 26.26 ms
         Context "5 listeners"
            Case "#1" : 5 runs - average runtime: 56.72 ms

@jerch fixed 😃