Everything in this .pk3dir is licensed under the GPL V2.
Two example skyboxes are included:

textures/skies/smudge:
Which is a LDR, single cubemap, skybox.

textures/skies/dune:
Which is HDR capable. So depending on the irisadaption level the sky will
darken, or brighten. r_hdr_irisadaption needs to be set to 1.

textures/skies/recotta:
Which is an LDR night-sky. A map using this does not need a light_environment
entity to light the scene. The compiler will approximate even lighting for the
entire level based around said sky.

textures/skies/yukongold:
Which is a skybox with a background, clouds rendered on top, with another
foreground box layered on top of the clouds. This is so the clouds can go
behind mountains or whatever you'd like.