One of the first surprises most people encounter when hosting their website on github pages is that jekyll doesn't work quite the as they expect. This is because they run a safe mode jekyll configuration with a whitelist of plugins for you to use. Since jekyll generates a static website, this is easy to work around by just generating your website locally and then pushing just the static site to github pages.
Then create your jekyll site in a new branch of your repository. This is where you will make future changes to the site.
To deploy your site to github pages, you can perform the following steps or just put them in a shell script for repeated use.
jekyll build cp ./_config.yml ./_site/_config.yml cp ./CNAME ./_site/CNAME cd _site git init git add --all git commit -m "update" git push -f https://github.com/agradl/agradl.github.io.git master cd ../ rm -rf _site
Note: if this is for a project page, then instead of pushing to the master branch, you should be pushing to the gh-pages branch.