Advise Users to Check for Machine-Specific Architecture Flags

[mfrankel923]

I wanted to recommend that in the instructions/documentation for compiling using the makefile that users check for machine-specific architecture flags. In the past, I compiled epanetmsx on a supercomputing cluster, and had initially had very slow run times because I was not aware of the modifications I needed to make to the makefile. After updating the makefile with the correct architecture flag, the runtime of epanetmsx was as I expected (much faster).

When fixing this issue, here are resources I found helpful:

https://stackoverflow.com/questions/45933732/how-to-specify-a-compiler-in-cmake
https://stackoverflow.com/questions/11783932/how-do-i-add-a-linker-or-compile-flag-in-a-cmake-file

And here is the modification I made to the makefile in my case:

SET(CMAKE_C_COMPILER "icc")
SET(CMAKE_C_FLAGS "-xCORE-AVX2 -axCORE-AVX512,MIC-AVX512")