The firm I recently stated working at just moved to Git and I am the only resource then knows Git. I get asked so many times a day on how to mirror a git repostory.
From the birds eyes very its very easy:
git clone –mirror email@example.com:project project
git remote add github firstname.lastname@example.org:username/project.git
In cron Job
cd /pathto/project && git fetch -q && git push -q –mirror github
Thats how easy it is to mirror a Git Project on to GitHub