nixos-render-docs: add structural includes, use for manual

this adds support for structural includes to nixos-render-docs.
structural includes provide a way to denote the (sub)structure of the
nixos manual in the markdown source files, very similar to how we used
literal docbook blocks before, and are processed by nixos-render-docs
without involvement of xml tooling. this will ultimately allow us to
emit the nixos manual in other formats as well, e.g. html, without going
through docbook at all.

alternatives to this source layout were also considered:

a parallel structure using e.g. toml files that describe the document
tree and links to each part is possible, but much more complicated to
implement than the solution chosen here and makes it harder to follow
which files have what substructure. it also makes it much harder to
include a substructure in the middle of a file.

much the same goes for command-line arguments to the converter, only
that command-lined arguments are even harder to specify correctly and
cannot be reasonably pulled together from many places without involving
another layer of tooling. cli arguments would also mean that the manual
structure would be fixed in default.nix, which is also not ideal.

nixos/doc/manual/administration/containers.chapter.md

@@ -21,8 +21,8 @@ which is often not what you want. By contrast, in the imperative
 approach, containers are configured and updated independently from the
 host system.
 
-```{=docbook}
-<xi:include href="imperative-containers.section.xml" />
-<xi:include href="declarative-containers.section.xml" />
-<xi:include href="container-networking.section.xml" />
+```{=include=} sections
+imperative-containers.section.md
+declarative-containers.section.md
+container-networking.section.md
 ```

nixos/doc/manual/administration/running.md

@@ -0,0 +1,14 @@
+# Administration {#ch-running}
+
+This chapter describes various aspects of managing a running NixOS system, such as how to use the {command}`systemd` service manager.
+
+```{=include=} chapters
+service-mgmt.chapter.md
+rebooting.chapter.md
+user-sessions.chapter.md
+control-groups.chapter.md
+logging.chapter.md
+cleaning-store.chapter.md
+containers.chapter.md
+troubleshooting.chapter.md
+```

nixos/doc/manual/administration/running.xml

@@ -1,21 +0,0 @@
-<part xmlns="http://docbook.org/ns/docbook"
-      xmlns:xlink="http://www.w3.org/1999/xlink"
-      xmlns:xi="http://www.w3.org/2001/XInclude"
-      version="5.0"
-      xml:id="ch-running">
- <title>Administration</title>
- <partintro xml:id="ch-running-intro">
-  <para>
-   This chapter describes various aspects of managing a running NixOS system,
-   such as how to use the <command>systemd</command> service manager.
-  </para>
- </partintro>
- <xi:include href="../from_md/administration/service-mgmt.chapter.xml" />
- <xi:include href="../from_md/administration/rebooting.chapter.xml" />
- <xi:include href="../from_md/administration/user-sessions.chapter.xml" />
- <xi:include href="../from_md/administration/control-groups.chapter.xml" />
- <xi:include href="../from_md/administration/logging.chapter.xml" />
- <xi:include href="../from_md/administration/cleaning-store.chapter.xml" />
- <xi:include href="../from_md/administration/containers.chapter.xml" />
- <xi:include href="../from_md/administration/troubleshooting.chapter.xml" />
-</part>

nixos/doc/manual/administration/troubleshooting.chapter.md

@@ -3,10 +3,10 @@
 This chapter describes solutions to common problems you might encounter
 when you manage your NixOS system.
 
-```{=docbook}
-<xi:include href="boot-problems.section.xml" />
-<xi:include href="maintenance-mode.section.xml" />
-<xi:include href="rollback.section.xml" />
-<xi:include href="store-corruption.section.xml" />
-<xi:include href="network-problems.section.xml" />
+```{=include=} sections
+boot-problems.section.md
+maintenance-mode.section.md
+rollback.section.md
+store-corruption.section.md
+network-problems.section.md
 ```