Hints for kasts in community

Hints

• asv-custom-value-empty
  :85 -
  This custom value is empty.
• asv-unknown-tag
  :88 - developer
  Found invalid tag. Non-standard tags should be prefixed with `x-`. AppStream also provides the <custom/> tag to add arbitrary custom data to metainfo files. This tag is read by AppStream libraries and may be useful instead of defining new custom toplevel or `x-`-prefixed tags if you just want to add custom data to a metainfo file.