Hints for pipewalker in main

Hints

• asv-unknown-tag
  :19 - 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.
• asv-url-not-secure
  :32 - http://pipewalker.sourceforge.net/
  Consider using a secure (HTTPS) URL for this web link.