Hints for nitrokey-app in main

Hints

• asv-content-rating-missing
  com.nitrokey.nitrokey-app.appdata.xml -
  This component has no `content_rating` tag to provide age rating information. You can generate the tag data online by answering a few questions at https://hughsie.github.io/oars/
• asv-cid-contains-hyphen
  com.nitrokey.nitrokey-app.appdata.xml:3 - com.nitrokey.nitrokey-app
  The component ID contains a hyphen/minus. Using a hyphen is strongly discouraged, to improve interoperability with other tools such as D-Bus. A good option is to replace any hyphens with underscores (`_`).
• screenshot-no-thumbnails
  No thumbnails have been generated for screenshot 'https://raw.githubusercontent.com/Nitrokey/nitrokey-app/master/images/icon/nitrokey-app-icon-128-black.png'.
  This could mean that the original provided screenshot is too small to generate thumbnails from.