Fix and add some fields for Flare

The grammar of the summary was wrong (probably was copied when upstream was wrong, but this has already been updated there).

Also added links to Flatpak build recepies.

The screenhots are very outdated. If you want, I can send some uncensored and updated ones.

Finally, the "description" is not well-formatted, but I was not sure if the website allows bullet-lists.