How to build a Ghost distribution?

I have no experience of JS development, or the tools associated with it. However, I want to hack the code to try to get around the Mailgun obligation for news letters.

From a git clone of the code base, ow do I build a distribution? I tried installing Grunt, and execing
npm run build
but that failed for lack of a gruntfile in an empty directory.

What process do the Ghost distribution builders use?

Yes, I appreciate that. I may have to admit defeat by Ghost.