repository, readme, keywords and categories, so the crate page says what
this is and is findable; the MIT text the license field was already
claiming; and rust-version, because let-chains mean 1.88 and an older
toolchain should say so rather than fail to parse.
`cargo package` builds the packaged tarball cleanly: 17 files, nothing
stray, and the release binary links nothing beyond libc, so installing it
needs no system development packages.
