84b1c0c481
Since some time Nixos has firewall enabled by default, so update example. Also, remove newline escaping (it isn't needed). Closes https://github.com/NixOS/nixpkgs/issues/25174
To build the manual, you need Nix installed on your system (no need
for NixOS). To install Nix, follow the instructions at
https://nixos.org/nix/download.html
When you have Nix on your system, in the root directory of the project
(i.e., `nixpkgs`), run:
nix-build nixos/release.nix -A manual.x86_64-linux
When this command successfully finishes, it will tell you where the
manual got generated.