The current stage is only for learning and testing.
Use eselect-repository install and configuration this overlay:
At first we need install eselect-repository modules:
emerge --ask app-eselect/eselect-repository
eselect repository add yafa-overlay git https://github.com/yafa-xena/yafa-overlay
emaint sync --repo yafa-overlay
If you want to disable yafa-overlay and delete all contents, you can execute:
eselect repository remove -f yafa-overlay