Official Flatpak release

[Asghwor]

Having an official Flatpak release would make it easier to install this app on any system, since there wouldn't be a need to manually unzip it, create a desktop entry and solve any dependency problems that may arise, such as #82.

It would also make it easier for people to learn about it.

[Asghwor]

I've created an unofficial Flatpak package and submitted it on Flathub, as mentioned in #85.

I hope the dev might consider taking it over if they resume development in the project.