Add warning that EnvLogger currently works only on Linux.
Add warning that EnvLogger currently works only on Linux.

PiperOrigin-RevId: 387667347
Change-Id: I05feb0fe8a18a63d9b7ce6889ef23982d2ea1eec

deepmind/envlogger,deepmind/envlogger,deepmind/envlogger,deepmind/envlogger