Distribute Psst through Flathub

It would be great to have Psst build as Flatpak and distributed through Flathub (the most popular Flatpak store).

Flatpaks, and in particular Flathub as a package "store" are becoming more popular and adopted in many Linux distributions. Some distributions, like Fedora Silverblue, even use an immutable system, which means the recommended way of installing packages is via Flathub to avoid layering unnecessary packages on the system.