manual: add nixos-rebuild build-image section

nixos/doc/manual/installation/building-images-via-nixos-rebuild-build-image.chapter.md

@@ -0,0 +1,16 @@
+# Building Images with `nixos-rebuild build-image` {#sec-image-nixos-rebuild-build-image}
+
+Nixpkgs contains a variety of modules to build custom images for different virtualization platforms and cloud providers, such as e.g. `amazon-image.nix` and `proxmox-lxc.nix`.
+
+While those can be imported individually, `system.build.images` provides an attribute set mapping variant names to image derivations. Available variants are defined - end extendable - in `image.modules`, an attribute set mapping variant names to a list of NixOS modules.
+
+All of those images can be built via both, their `system.build.image` attribute, and the CLI `nixos-rebuild build-image`. To build i.e. an Amazon image from your existing NixOS configuration:
+
+```ShellSession
+$ nixos-rebuild build-image --image-variant amazon
+$ ls result
+nixos-image-amazon-25.05pre-git-x86_64-linux.vhd  nix-support
+```
+
+To get a list of all variants available, run `nixos-rebuild build-image` without arguments.
+

nixos/doc/manual/installation/building-nixos.chapter.md

@@ -1,7 +1,7 @@
 # Building a NixOS (Live) ISO {#sec-building-image}
 
 Default live installer configurations are available inside `nixos/modules/installer/cd-dvd`.
-For building other system images, [nixos-generators] is a good place to start looking at.
+For building other system images, see [Building Images with `nixos-rebuild build-image`](#sec-image-nixos-rebuild-build-image).
 
 You have two options:
 
@@ -14,8 +14,6 @@ on which they immediately depend in order to work correctly.
 However, if you are confident, you can opt to override those
 enforced values with `mkForce`.
 
-[nixos-generators]: https://github.com/nix-community/nixos-generators
-
 ## Practical Instructions {#sec-building-image-instructions}
 
 To build an ISO image for the channel `nixos-unstable`:

nixos/doc/manual/installation/installation.md

@@ -8,5 +8,6 @@ installing.chapter.md
 changing-config.chapter.md
 upgrading.chapter.md
 building-nixos.chapter.md
+building-images-via-nixos-rebuild-build-image.chapter.md
 building-images-via-systemd-repart.chapter.md
 ```

nixos/doc/manual/redirects.json

@@ -167,6 +167,9 @@
   "sec-building-image-tech-notes": [
     "index.html#sec-building-image-tech-notes"
   ],
+  "sec-image-nixos-rebuild-build-image": [
+    "index.html#sec-image-nixos-rebuild-build-image"
+  ],
   "sec-image-repart": [
     "index.html#sec-image-repart"
   ],