Yago is just another boring gentoo overlay.
Cloning the repository into your favorite directory:
# mkdir -p /usr/local/overlays
# cd /usr/local/overlays
# git clone git://github.com/tled/yago.git
Add to /etc/portage/make.conf:
PORTDIR_OVERLAY="
/usr/local/yago
${PORTDIR_OVERLAY}
"