Nix shell
The first file shell.nix is a standard shell.nix file for nixos.
The second one create a FHSUserEnv to symlink the static dependency under /usr/share/javascript, in order to work around the harcoded static path in settings/base.py.
shell.nix was previously under .gitignore, but providing a ready shell.nix make it easier for new devs using nixos to join the project.