Options/Parser: debugVersionOpt: comment: add nix-build note

[Anton-Latukha]

Remark deserves a comment note in the source code.

[alexfmpe]

Ran into this exact issue on a --version for a CLI.
One can workaround by wrapping the executable and passing git data as environment variables:

root = ./.;

exe = nixpkgs.writeScript "my-package-exe" ''
  #!/usr/bin/env bash
  set -euo pipefail
  export REV=$(git -C ${root} rev-parse HEAD)
  export BRANCH=$(git -C ${root} rev-parse --abbrev-ref HEAD)
  ${nixpkgs.haskell.lib.justStaticExecutables pkgs.my-package}/bin/my-package $@
';

[alexfmpe]

Downside is that it breaks --version for nix-shell cabal, though maybe more wrapping could fix that