Deactivated cores not showing up

[AlixBernard]

Cores that are deactivated before starting the app do not show up. This can be done manually (eg. by running sudo su -c "echo 0 > /sys/devices/system/cpu/cpu1/online") or via the app:

• launch through the terminal
• deactivate any cores
• close the terminal (or run ctrl+C in the terminal then close the app)
• restart the app (less cores are displayed)

Possible solutions:

• displaying a warning stating that more cores are detected in the path /sys/devices/system/cpu/ and explain how to activate them if required
• detect the number of cores via the path /sys/devices/system/cpu/ instead of os.cpu_count()

I can make a PR for either of those solutions, let me know what you think is best.

Edit: changed cpu0 to cpu1 as cpu0 cannot be turned off.