message: Updated README to reflect deprecation of rustup install
diff: @@ -61,7 +61,7 @@ If `rustup` says the `miri` component is unavailable, that's because not all
  nightly releases come with all tools. Check out
  [this website](https://rust-lang.github.io/rustup-components-history) to
  determine a nightly version that comes with Miri and install that using
  -`rustup install nightly-YYYY-MM-DD`.
  +`rustup toolchain install nightly-YYYY-MM-DD`.
  Now you can run your project in Miri:
  