I ran into this problem just now while setting up this very blog, which means we’re off to a great start.
The problem was that I needed to create a new Jekyll site, but inside the repo:
cd ~/Code/barbeque.github.io jekyll new .
That is, the site needs to be created at the base of your repository. Most of the tutorials seem to skip the step where you create a new Jekyll site or are ambiguous about where you put it.
If you get an error about there already being stuff in the directory, use
jekyll new, or clean the directory out (my preference).