That’s a great question; there is an overwhelming amount of front end tools out there. I got started learning how to use webpack by doing simple tutorials that focused on webpack; same with grunt and gulp. You can find a number of tutorials that will teach you the basics of how to get started with these tools.
Sometimes this will be enough to get you started with setting up the development environments of the Open Source project. If not, then the README might include more detailed instructions for how to get started. If they don’t, then don’t be shy about recommending that instructions be added to the README.