Bootstrap 4 release - create custom css
I am trying to figure out how to build a custom css for B4 released version. I have downloaded source files but don't see a Gruntfile.js that I used for v4.alpha6. I am looking at: V4 doc which says: Should you require build tools, they are included for developing Bootstrap and its docs, but they’re likely unsuitable for your own purposes. So, what do I use for my own purposes? How do I build a custom css? I see that I have to create my own _custom.scss file, but I am not sure about the Gruntfile.js . I copied the one from alpha6 version, but it's not running. I am getting this: D:\Bootstrap4