Add repology badge to the website?

**Small badge**  
[![Packaging status](https://repology.org/badge/tiny-repos/duff.svg)](https://repology.org/project/duff/versions)

**Long badge**  
[![Packaging status](https://repology.org/badge/vertical-allrepos/duff.svg)](https://repology.org/project/duff/versions)
