Add shell.nix example

book/index.adoc

@@ -89,12 +89,19 @@ Ecosystem of tools - e.g. Home Manager.
 [[dev_shells]]
 = What are dev shells?
 
+[,nix]
+----
+# shell.nix
+
+include::../shell.nix[]
+----
+
 [[direnv]]
 = dev shells and direnv
 
 Using a local flake:
 
-[source,bash]
+[,bash]
 ----
 use flake .
 ----

shell.nix

@@ -0,0 +1,11 @@
+{
+  pkgs ? import <nixpkgs> { },
+}:
+
+pkgs.mkShell {
+  packages = with pkgs; [
+    php
+    phpPackages.composer
+    phpactor
+  ];
+}