[Feature Request]: Create a Flatpak version

[Nitrousoxide]

Currently, there are a couple of ways you can deploy the reader, via Snap and via a source build. Flatpak provides the runtime and build time consistency needed to ensure the app will work properly in a variety of environments like Snap. Flatpak, and Flathub are both widely supported in a variety of distros, with many such as Fedora moving more and more native packages to them as major releases increment.

Additionally, Flathub has the tools to enable automated builds and pushes to their repos, making additional support beyond initial setup minimal for continued version pushes.

Providing a flatpak version will help to expand the userbase and may encourage more engagement with the project's repo as well.