Cloning this repository:

git clone git://gitorious.org/~viridior/gentoo-arm-overlay/viridior-gentoo-arm-overlay.git viridior-gentoo-arm-overlay
cd viridior-gentoo-arm-overlay

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

git remote add viridior-gentoo-arm-overlay git://gitorious.org/~viridior/gentoo-arm-overlay/viridior-gentoo-arm-overlay.git
git fetch viridior-gentoo-arm-overlay
git checkout -b my-local-tracking-branch viridior-gentoo-arm-overlay/master_or_other_branch