neuron-notes: create a top-level attribute for haskellPackages.neuron

The obvious choice, "neuron", is already taken by a python package, so I called
it "neuron-notes" instead. If anyone has a better suggestion how to call this
entry, please let me know.

pkgs/top-level/all-packages.nix

···
 
   ngrep = callPackage ../tools/networking/ngrep { };
 
+  neuron-notes = haskell.lib.justStaticExecutables (haskell.lib.generateOptparseApplicativeCompletion "neuron" haskellPackages.neuron);
+
   ngrok = ngrok-2;
 
   ngrok-2 = callPackage ../tools/networking/ngrok-2 { };