Make sure /etc/portage/repos.conf directory exists and dev-vcs/git installed.
curl https://raw.githubusercontent.com/aaaaadrien/adrien-overlay/master/repo.conf -o /etc/portage/repos.conf/adrien-overlay.conf
Make sure /etc/portage/repos.conf directory exists, and make sure dev-vcs/git and app-eselect/eselect-repository installed.
eselect repository add adrien-overlay git https://github.com/aaaaadrien/adrien-overlay.git
Make sure dev-vcs/git and app-portage/layman installed on your system
curl https://raw.githubusercontent.com/aaaaadrien/adrien-overlay/master/repositories.xml -o /etc/layman/overlays/adrien-overlay.xml
layman -S
layman -a adrien-overlay
To enable updates from my overlay, set to ON the cl_update_other_set with
cl-core-variables --set update.cl_update_other_set=on