If you want to publish your root user page, which appears at / (e.g. github.com/cirosantilli/cirosantilli.github.io for the user cirosantilli), GitHub annoyingly forces you to use the master branch for the HTML output:
This means that you must place your .bigb input files in a branch other than master to clear up master for the generated HTML.
ourbigbook automatically detects if your repository is a root repository or not by parsing git remote output, but you must setup the branches correctly yourself.
So on a new repository, you must first checkout to a different branch as in:
git init
git checkout -b dev
or to move an existing repository to a non-master branch:
git checkout -b dev
git push origin dev:dev
git branch -D master
git push --delete origin master
You then will also want to set your default repository branch to dev in the settings for that repository: help.github.com/en/github/administering-a-repository/setting-the-default-branch