Hard-coded number of cores

[JavierSanchez-Utges]

The number of cores is hard coded and if unchanged, the execution might get killed:

GrASP/parse_files.py

Line 694 in 75986d7

num_cores = 24

Perhaps it would be better if there was an argument to specify this, or warn the user on the README.

It happened to me, now edited the code to use 8 cores, and all good.

Thanks!