We ran bookbinder generate as outlined in the readme, but ended up with a site that had no content at the root level (no main index.html).
On closer inspection, we found that the master_middleman/source directory contains index.html.md and not index.html.erb. Renaming this file to index.html.erb helped.
We think this is a small error with the generate subcommand, but we did not have time to dive into this.
Dirk & Dan