Update all examples and results for fast comes first

[JuanitoFatas]

Update template:

require 'benchmark/ips'

def fast
end

def slow
end

Benchmark.ips do |x|
  x.report('fast') { fast }
  x.report('slow') { slow }
  x.compare!
end

and reorganize all stuff according to 👆 👆 👆

Since x.compare! will show fast then slow, this may have a better reading experience when reading README IMO. Also document in CONTRIBUTING.md to give people notice when submits a new entry.

[mateusdeap]

I'll be taking this