First fork WooCommerce to one of your channels through github.com/woothemes/woocommerce/fork_select

Use the GitHub client (for Windows or Mac OS X) to sync with a local directory, or clone your repostitory by hand.

Enter the console in the WooCommerce fork directory and run the following commands to add extra sources:
git remote add upstream git://github.com/woothemes/woocommerce.git

Merge upstream with the current working directory
git fetch upstream
git merge upstream/master

And put it all online:
git push origin master