pytorch-reader: README lists three containers, lib.rs documents four

crates/pytorch-reader/README.md says the crate reads three containers:

It reads every container torch.save has written: the ZIP archive of PyTorch 1.6 and later, the legacy pickle stream of 0.1.10 through 1.5, and the TAR archive before that.

src/lib.rs documents four, adding the plain pickle that from_reader and load_config handle. The README is what crates.io shows, so it should match; a one-clause addition.

While there: the README's code block is not compiled (lib.rs does not include_str! it), so its bare ? at top level is fine today, but it would break the moment someone wires the README in as the crate doc. Wrapping it the way the lib.rs example is (# Ok::<(), Box<dyn std::error::Error>>(())) costs nothing and removes the trap.