please include a LICENSE file in git repository and in published crates
This project's Cargo.toml file specifies that the sop crate is published under the terms of an MIT license, but most (if not all) variants of the MIT license require that the actual text of the license is shipped with redistributed sources (e.g. sources published to and distributed by crates.io, or by linux distributions) - c.f. the MIT license entries on choosealicense.com or opensource.org.
Additionally, there are many variants of the MIT license that all have subtly different terms (the Fedora Project recognises over 20 different variants here), so only the inclusion of an actual LICENSE text in a dedicated file distinguishes the actual MIT variant.
Most Rust projects I have seen choose the variant of MIT license that the Fedora Project classifies as Modern_Style_with_sublicense - c.f. the LICENSE file included with the futures crate.