AppImage builds for Discord Stable, Discord PTB, and Discord Canary. These AppImages are built using the discord-appimage.sh script with dependencies pulled from Ubuntu 20.04's repositories.
To use an AppImage, just download it, chmod a+x the AppImage file, then run it!
The AppImages listed on the releases page do not actually contain the Discord client, but will build the full AppImage containing the client on first run. After the full AppImage has been built, the AppImage downloaded from the releases page can be deleted. The file size of the full AppImage build will be around 100MB.