[rdyott]

I don't have it in the official repo, how can I install this skin?

Google for Kodi Lyrebird skin GitHub 😎
https://github.com/Rufoo/skin.lyrebird/b.../readme.md 

It's there a guide on how to install this? 

when you download the file. you will need to do some steps....
1- rename the file. (REMOVE the word "master" from it)
2- open the zip file and do the same with the folder file inside. remove "master"

then go into your kodi, and go to addons, and "install from Zip" and navigate to where you downloaded the file.
kodi should then unzip the zip file and activate the skin in your UI. and you can then start using it.