With Gentoo repos.conf:

sudo /bin/bash -c 'echo "[ace-overlay]
location = /usr/local/portage/ace-overlay
sync-type = git
sync-uri = https://git.geekhome.org/ace/ace-overlay
auto-sync = yes
clone-depth = 0" > /etc/portage/repos.conf/ace-overlay.conf'

With Layman:

curl -k --request GET "https://git.geekhome.org/ace/ace-overlay/raw/branch/master/ace-overlay.xml" 2>/dev/null > /tmp/ace-overlay.xml

sudo layman -o file:///tmp/ace-overlay.xml -f -a ace-overlay