doc: clarify whether @time allocations include compilation

[jariji]

@time says

A macro to execute an expression, printing the time it took to execute, the number of allocations, and the total number of bytes its execution caused to be allocated, before returning the value of the expression.

It's not obvious to me whether compilation allocations are included in "execution" (is that the same as "evaluation"?).

[KristofferC]

This is also in the docs for @time:

In some cases the system will look inside the @time expression and compile some of the called code before execution of the top-level expression begins. When that happens,
some compilation time will not be counted. To include this time you can run @time @eval ....