The supplied flatpak manifest org.cataclysmdda.CataclysmDDA.json will
download and build the latest release of Cataclysm-DDA.  An app built in
this way should be available on flathub:

  https://flathub.org/apps/detail/org.cataclysmdda.CataclysmDDA

Check the flatpak documentation at http://docs.flatpak.org for
information on how to customise the manifest, build your own copies of
the app, and install or distribute them.
