Hints for gretl in main

Errors

• missing-desktop-file
  Found an AppStream metainfo XML file, but the associated .desktop file is missing. This often happens when the .desktop file is renamed, but the <launchable type="desktop-id"/> tag value of the AppStream metainfo file is not adapted as well, or if the metainfo file is located in a different package than the .desktop file.
  Please fix the packaging or work with upstream to resolve this issue.
  For older metadata, the desktop-id is inferred from the <id/> tag. If the component metadata has no launchable tag and no icon tag of type stock, check if a .desktop file named after the component-ID is located in the same package.