Update bert readme: uses correct tf-nightly pip package
Update bert readme: uses correct tf-nightly pip package

PiperOrigin-RevId: 279631484

alexgorban/models,alexgorban/models,tombstone/models,alexgorban/models,alexgorban/models,tombstone/models,tombstone/models,tombstone/models,tombstone/models,tombstone/models,alexgorban/models