Mention `--accept-flake-config` in the related warning
Mention `--accept-flake-config` in the related warning

Make sure that people who run Nix in non-interactive mode (and so don't have the possibility to interactively accept the individual flake configuration settings) are aware of this flag.

Fix #7086
NixOS/nix,NixOS/nix,NixOS/nix,NixOS/nix,NixOS/nix