Cloning this repository:

git clone git://gitorious.org/processing-emacs/processing-emacs.git processing-emacs
cd processing-emacs

Add this repository as a remote to an existing local repository:

git remote add processing-emacs git://gitorious.org/processing-emacs/processing-emacs.git
git fetch processing-emacs
git checkout -b my-local-tracking-branch processing-emacs/master_or_other_branch