message: fix README install instructions
diff: @@ -56,7 +56,7 @@ compiled the right way.
  Install Miri as a cargo subcommand:
  ```sh
  -cargo +nightly install --git https://github.com/solson/miri/
  +cargo +nightly install --git https://github.com/solson/miri/ miri
  ```
  Be aware that if you used `rustup override set` to fix a particular Rust version
  