Two weeks ago I was looking for this. This is the easiest way I found to do it:
heroku create myproject --stack cedar --buildpack https://github.com/pearkes/heroku-buildpack-static
heroku create myproject --stack cedar --buildpack https://github.com/pearkes/heroku-buildpack-static
I was also experimenting with a Pelican buildpack (a python Jekyll): https://github.com/pearkes/heroku-buildpack-pelican
You deploy you markdown files and it generates your html in the deploy process.