fix broken link

service/documentation.md

@@ -361,6 +361,8 @@ Staff hours, hosting costs shadowed by GitLab.
    minutes without caching
  * [zola](https://www.getzola.org/): rust
 
+[Nanoc]: https://nanoc.ws/
+
 ### Testing
 
 To use those tests, we'd need to switch the wiki into a Git