To install this overlay, add URL to your /etc/layman.cfg:  
>(https://blshadow.org.ru/overlays.xml)  
Example:
```
overlays  : http://www.gentoo.org/proj/en/overlays/repositories.xml
            https://another-repo.tld/repo.xml
            https://blshadow.org.ru/overlays.xml
```
Then you need to add repo by layman:
```
layman -f && layman -a smoverlay
```