It's required to have the latest stable portage version installed. Older versions will not be supported in any case. Get the overlay first and afterwards install the qrtools package.

Create a repo config file in  /etc/portage/repos.conf/  with the following content:

[qlinux]
master = gentoo
location = /var/portage/qlinux
#sync-type = rsync
#sync-uri = rsync://downloads.dyndn.es/qrtools
sync-type = git
sync-uri = https://gitlab.com/kaili/qlinux.git
auto-sync = yes

Get the repository by syncing it:

$> emerge --sync qlinux

Install the qrtools package:

$ emerge qrtools

Now go to  /etc/portage/repos.conf  and rename the new config file

$ mv eselect-repo.conf qlinux.conf