nix: create wrapper around nix-shell

[strager]

Inspiration: https://github.com/teaxyz/cli

Samples:

# before
nix-shell -p pandoc --run 'pandoc doc.md -o doc.html'

# after
try pandoc doc.md -o doc.html

# before
nix-shell -p 'python3.withPackages (pythonPackages: [ pythonPackages.pygments pythonPackages.pyyaml ])' --run '~/tmp/Projects/llvm-project/llvm/tools/opt-viewer/opt-viewer.py --source-dir . --output-dir build-perf/opt-viewer/ build-perf/'

# after
try +python3/pygments/pyyaml ~/tmp/Projects/llvm-project/llvm/tools/opt-viewer/opt-viewer.py --source-dir . --output-dir build-perf/opt-viewer/ build-perf/