You'd need cc65 installed. I'm using v2.18, but the newer versions should work the same. In Windows you might as well install Windows Subsystem For Linux and use "make". But if you wanted to do it manually, or create a batch file, there's only four commands in the makefile. They're in reverse order. cc65 goes from slaughter.c to slaughter.s, ca65 goes from slaughter.s to slaughter.o, ca65 goes from reset.s to reset.o, and ld65 combines the .o files into slaughter.nes.
... I forgot to include a ROM in the update, didn't I. Lemme fix that real quick.