docs: add recursive method for fetching flake input out paths

The previous example would not work for flakes that have inputs with inputs of their own, leading to installation failures when attempting to install without internet access

Author: different-name

docs/disko-install.md

@@ -197,8 +197,19 @@ Add this to your flake.nix output:
 ```nix
 # `self` here is referring to the flake `self`, you may need to pass it using `specialArgs` or define your NixOS installer configuration
 # in the flake.nix itself to get direct access to the `self` flake variable.
-{ pkgs, self, ... }:
+{ lib, pkgs, self, ... }:
 let
+  flakeOutPaths =
+    let
+      collector =
+        parent:
+        map (
+          child:
+          [ child.outPath ] ++ (if child ? inputs && child.inputs != { } then (collector child) else [ ])
+        ) (lib.attrValues parent.inputs);
+    in
+    lib.unique (lib.flatten (collector self));
+
   dependencies = [
     self.nixosConfigurations.your-machine.config.system.build.toplevel
     self.nixosConfigurations.your-machine.config.system.build.diskoScript
@@ -210,7 +221,7 @@ let
     self.nixosConfigurations.your-machine.pkgs.perlPackages.FileSlurp
 
     (self.nixosConfigurations.your-machine.pkgs.closureInfo { rootPaths = [ ]; }).drvPath
-  ] ++ builtins.map (i: i.outPath) (builtins.attrValues self.inputs);
+  ] ++ flakeOutPaths;
 
   closureInfo = pkgs.closureInfo { rootPaths = dependencies; };
 in