Update benchmark.php

[AmiiirCom]

Adding grading and rating to the Total result (grading adjectives and coloring properties can be better😉)

[odan]

Thanks for your contribution. The thing is that the result ($total) is an absolute number to compare the performance of different servers. The idea is to not rate this result, because of the missing context. It would also mean that this baseline must be regularly updated to reflect improvement in server technology.