chore: add license cargo metadata (oops)

Cargo.toml

@@ -10,6 +10,7 @@ version = "0.1.0"
 edition = "2021"
 rust-version = "1.57.0"
 author = "Eliza Weisman <eliza@buoyant.io>"
+license = "MIT"
 repository = "https://github.com/hawkw/thingbuf"
 homepage = "https://github.com/hawkw/thingbuf"
 description = """