How to install this overlay

Layman

layman -a reagentoo

or

layman -o 'https://github.com/reagentoo/gentoo-overlay/raw/master/repositories.xml' -f -a reagentoo

Manually

Add an entry to /etc/portage/repos.conf:

[reagentoo]
location = /usr/local/portage/reagentoo
sync-uri = https://github.com/reagentoo/gentoo-overlay.git
sync-type = git
auto-sync = yes