message: add readme key to cargos manifest.
  This should make the readme display on cargos crates.io page
diff: @@ -9,6 +9,7 @@ license = "MIT OR Apache-2.0"
  homepage = "https://crates.io"
  repository = "https://github.com/rust-lang/cargo"
  documentation = "https://docs.rs/cargo"
  +readme = "README.md"
  description = """
  Cargo, a package manager for Rust.
  """
  