Add flathub verification token to gpodder.org

[tpikonen]

Flathub now allows applications to be verified by adding a file with a token to the project website. It would be nice to get a verification badge to gPodder in flathub.

Could we add the token to https://gpodder.gpodder.org/.well-known/org.flathub.VerifiedApps.txt somehow? There is a redirect from https://gpodder.gpodder.org/ to https://gpodder.github.io but this perhaps does not work with deep links. Maybe #6 needs to be fixed before this can be done?