Hints for font-viewer in main

Hints

• asv-nonstandard-gnome-extension
  :72 - kudos
  This tag is a GNOME-specific extension to AppStream and not part of the official specification. Do not expect it to work in all implementations and in all software centers.
• asv-url-not-secure
  :136 - http://fontmanager.github.io/
  Consider using a secure (HTTPS) URL for this web link.