message: document how to get a toolchain with clippy
diff: @@ -28,6 +28,11 @@ install that exact version of rustc as a toolchain:
  This will set up a rustup toolchain called `miri` and set it as an override for
  the current directory.
  +If you want to also have `clippy` installed, you need to run this:
  +```
  +./rustup-toolchain "" -c clippy
  +```
  +
  [`rustup-toolchain-install-master`]: https://github.com/kennytm/rustup-toolchain-install-master
  ## Building and testing Miri
  