It uses a makefile, you can just type make while in the pride-system-icon directory.
On Windows you may need to install GNU make first.
You'll need to have Go installed, I've added a vendor directory to make it easier. The compiled files will be placed in dist/windows/prideicon.exe and dist/linux/prideicon
Here are the commands to compile without using make:
go build -mod vendor -tags linux -o prideicon go build -mod vendor -tags windows -ldflags -H=windowsgui -o prideicon.exe