Add "Flathub" (Flatpak) as desktop application download option for Linux

When you're on the Discord home page <https://discord.com/>, there's a button to download the Discord desktop application.

With Linux it offers the choices "deb" and "tar.gz".

However, since for a few months now (early 2024?) you've been officially supporting Discord distribution on Flathub, could you add the "Flathub" choice with the <https://flathub.org/apps/com.discordapp.Discord> link? This will simplify access to this choice, and allow more people to discover it.

Similarly, when you're logged in, in the list of applications, "Flathub" is also missing.