If your /etc/portage/repos.conf is a directory, ten simply create a file called pazuzu.conf with the following contents:

[pazuzu]
location = /var/db/repos/pazuzu

sync-type = git
sync-uri = https://gitlab.fi.muni.cz/xlacko1/pazuzu-overlay
auto-sync = yes

Then, synchronize this repository:

emerge --sync pazuzu

# optionally update eix database:
eix-update

If your /etc/portage/repos.conf is a regular file, append the aforementioned configuration to it.