Add link and date to song example

go/blog/blog.yaml

  content: By [@empartridge](http://empartridge.tumblr.com).
  type: image
- url: file:///home/lu/m/musique/DRALMS/Shook/05 - Shook.mp3
  content: Shook, by DRALMS.
  content: Shook, by [DRALMS](https://dralms.bandcamp.com/).
  date: "2016-09-25"
  type: song