Create a new folder under /site/themes/yourthemename, then run brunch new -s https://github.com/octopuscreative/brunch-statamic. Next, open up brunch-config.coffee and update the themeName var on line 1. You're done!
Simple use npm start to kick off the compilation watchers + dev server, and use npm run build to run everything through a one off build step including minification and browser prefixing.
Coffeescript, Sass, Autoprefixer, Minification, Live Reload. Yep, all the good stuff.