Documentation ofos.copy_file_range needs a few updates:

1. Since Linux kernel 5.3 files pointed bysrc anddst no longer must reside in the same filesystem according tothe manual page.
2. There isa known issue for special filesystems like procfs and sysfs that should be noted.
3. It should documented that the function may implicitly utilize reflinks and server-side copy.

This was requested in#93152 (comment).