message: explain our shell encoding
diff: @@ -340,6 +340,11 @@ path = "lib.rs"
  let sysroot = if is_host { dir.join("HOST") } else { PathBuf::from(dir) };
  std::env::set_var("MIRI_SYSROOT", &sysroot); // pass the env var to the processes we spawn, which will turn it into "--sysroot" flags
  if print_env {
  + // Escape an arbitrary string for the shell: by wrapping it in `'`, the only special
  + // character we have to worry about is `'` itself. Everything else is taken literally
  + // in these strings. `'` is encoded as `'"'"'`: the outer `'` end and being a
  + // `'`-quoted string, respectively; the `"'"` in the middle represents a single `'`.
  + // (We could use `'\''` instead of `'"'"'` if we wanted but let's avoid backslashes.)
  println!("MIRI_SYSROOT='{}'", sysroot.display().to_string().replace('\'', r#"'"'"'"#));
  } else if !ask_user {
  println!("A libstd for Miri is now available in `{}`.", sysroot.display());
  