add Pruism feed to fdroid.ini

Purisms librem.one have announced to publish their Android Apps on F-Droid. see: https://librem.one/

Will you release your apps on F-Droid? Yes! In the meantime, any app that speaks our open protocols will work. We recommend: Riot for chat, Tusky for social and K-9 Mail for mail.

If I'm not mistaken this should qualify them for: https://gitlab.com/fdroid/planet/wikis/Inclusion-Rules