Adds an environment/background to Stardust XR!

If you installed the Stardust XR server via:

sudo dnf group install stardust-xr

Or if you installed via the installation script, Atmosphere comes pre-installed

atmosphere install default_envs/the_grid # or any other folder with an env.kdl file inside it
atmosphere set-default the_grid
atmosphere show # the_grid implied since set to default

To make your own, follow the comments and structure of the the_grid environment in this repo.