nixos/doc: small rephrase in documentation of documentation

## Contributing to `nixos-*` tools' manpages {#sec-contributing-nixos-tools}

The manual pages for the tools available in the installation image can be found in Nixpkgs' by running (e.g for `nixos-rebuild`):

The manual pages for the tools available in the installation image can be found in Nixpkgs by running (e.g for `nixos-rebuild`):

```ShellSession

$ git ls | grep nixos-rebuild.8

```

Man pages are written in [`mdoc(7)` format](https://mandoc.bsd.lv/man/mdoc.7.html) and should be portable between mandoc and groff for rendering (though minor differences may occur, mandoc and groff seem to have slightly different spacing rules.)

Man pages are written in [`mdoc(7)` format](https://mandoc.bsd.lv/man/mdoc.7.html) and should be portable between mandoc and groff for rendering (except for minor differences, notably different spacing rules.)

For previewing edited files, you can just run `man --local-file path/to/file.8` and you will see it rendered.

For a preview, run `man --local-file path/to/file.8`.

Being written in `mdoc`, these manpages use semantic markup. This file provides a guideline on where to apply which of the semantic elements of `mdoc`.

Being written in `mdoc`, these manpages use semantic markup. This following subsections provides a guideline on where to apply which semantic elements.

### Command lines and arguments {#ssec-contributing-nixos-tools-cli-and-args}

In any manpage, commands, flags and arguments to the *current* executable should be marked according to their semantics. Commands, flags and arguments passed to *other* executables should not be marked like this and should instead be considered as code examples and marked with `Ql`.

- Use `Fl` to mark flag arguments, `Ar` for their arguments.

- Repeating arguments should be marked by adding ellipses (`...`).

- Repeating arguments should be marked by adding an ellipsis (spelled with periods, `...`).

- Use `Cm` to mark literal string arguments, e.g. the `boot` command argument passed to `nixos-rebuild`.

- Optional flags or arguments should be marked with `Op`. This includes optional repeating arguments.

- Required flags or arguments should not be marked.

- Mutually exclusive groups of arguments should be enclosed in curly brackets, preferably created with `Bro`/`Brc` blocks.

When an argument is used in an example it should be marked up with `Ar` again to differentiate it from a constant. For example, a command with a `--host name` flag that calls ssh to retrieve the host's local time would signify this thusly:

When an argument is used in an example it should be marked up with `Ar` again to differentiate it from a constant. For example, a command with a `--host name` option that calls ssh to retrieve the host's local time would signify this thusly:

```

This will run

.Ic ssh Ar name Ic time

Generated paths, e.g. `result/bin/run-hostname-vm` (where `hostname` is a variable or arguments) should be marked as `Ql` inline literals with their variable components marked appropriately.

 - Taking `hostname` from an argument become `.Ql result/bin/run- Ns Ar hostname Ns -vm`

 - Taking `hostname` from a variable otherwise defined becomes `.Ql result/bin/run- Ns Va hostname Ns -vm`

 - When `hostname` refers to an argument, it becomes `.Ql result/bin/run- Ns Ar hostname Ns -vm`

 - When `hostname` refers to a variable, it becomes `.Ql result/bin/run- Ns Va hostname Ns -vm`

### Code examples and other commands {#ssec-contributing-nixos-tools-code-examples}

```

.Bd -literal -offset indent

{

  options.hostname = "\c

  config.networking.hostname = "\c

.Ar hostname Ns \c

";

}

    '';

  # Generate the configuration.nix manual package

  # Generate the `man configuration.nix` package

  nixos-configuration-reference-manpage = runCommand "nixos-configuration-reference-manpage"

    { nativeBuildInputs = [

        buildPackages.installShellFiles