Made for my specific install, which is 
Manjaro on a Thinkpad A485, but
it will work as long as your cores have descriptors.
You will either need systemd-ac-power or any other utility
that outputs a "yes" when you have the charger plugged in.
There are a couple options you can set through envvars, see the .env file.
You can either run this as sudo cpumgr & disown, or set it
up as a systemd service.
powertop reports around 10Wh draw with 8 cores enabled and
around 7Wh with only 4, so I get a ~30% longer battery life
by doing absolutely nothing \o/
Compilation is the standard go build -o nameofexecutable .
, install go with yay -S golang if you haven't already.