operating-systems: mention other Fedora Flavours and Ubuntu Spins

[Mikaela]

Description

Resolves: asked in the PrivacyTools Lounge at Matrix by @dngray based on my suggestion

Check List

• I understand that by not opening an issue about a software/service/similar addition/removal, this pull request will be closed without merging.
  • while I hope this is OK as I am not suggesting a new software/service/similar, just expanding the existing recommendations.
• I have read and understand the contributing guidelines.
  • it has been some time though, please tell me if I need to reread it :)
• The project is Free Libre and/or Open Source Software
  • should be if it's recommended in the first place

• Netlify preview for the mainly edited page: https://deploy-preview-1988--privacytools-io.netlify.app/operating-systems/#os

• Code repository of the project (if applicable): not applicable, already listed

[jonaharagon]

Thank you Mikaela :)