Hints for simple-scan in main

Warnings

• translations-not-found
  Unable to add languages information, even though a translation tag was present in the MetaInfo file. Please check that its value is set correctly, and all locale files are placed in the right directories (e.g. /usr/share/locale/*/LC_MESSAGES/ for Gettext .mo files).
• screenshot-download-error
  Error while downloading screenshot from 'https://gitlab.gnome.org/GNOME/simple-scan/raw/HEAD/data/screenshots/simple-scan-1.png': Failed to download file: CONNECT tunnel failed, response 403
  This might be a temporary server issue, or the screenshot is no longer available.