Change README to reflect latest API changes.
Change README to reflect latest API changes.

google/jimfs,wrmsr/jimfs,szpak/jimfs,rasheedamir/jimfs,wrmsr/jimfs,akkinenirajesh/jimfs,akkinenirajesh/jimfs,yaochang/jimfs,szpak/jimfs,rasheedamir/jimfs,thejavamonk/jimfs,yaochang/jimfs,google/jimfs