fix typo, --help argument does not exist

Author: Alexandre Peyroux

README.org

@@ -18,7 +18,7 @@ This will download and build =nix-tools=.
 
 #+begin_src sh
 nix build -f https://github.com/input-output-hk/haskell.nix/archive/master.tar.gz nix-tools -o nt
-./nt/bin/cabal-to-nix --help
+./nt/bin/cabal-to-nix
 #+end_src
 
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