diff --git a/README.markdown b/README.markdown
index 4060a8f..e077cda 100644
--- a/README.markdown
+++ b/README.markdown
@@ -2,9 +2,21 @@
 
 This repository contains files for building
 [financier](https://gitlab.com/mpuppe/financier/) with the
-[Nix](https://nixos.org/manual/nix/stable/) package manager.
+[Nix](https://nixos.org/manual/nix/stable/) package manager. We rely on the
+[Flakes](https://nixos.wiki/wiki/Flakes) feature of Nix. Make sure you have
+Flakes [enabled](https://nixos.wiki/wiki/Flakes#Installing_flakes) before you
+continue.
 
-First, you should update the necessary Nix files:
+## Module
+
+There is a module (available as flake output `nixosModule`) that you can use in
+your NixOS configuration. See [module.nix](./module.nix) for the available
+options. This is intended to be the primary way how to use this flake in your
+configurations.
+
+## Building the package
+
+First, you can (optionally) update the necessary Nix files:
 
 ``` bash
 nix develop --command bash generate.sh
@@ -16,5 +28,25 @@ Afterwards, the distribution for financier can be built:
 nix build
 ```
 
-There is also a module (module.nix) that you can use in your NixOS
-configuration.
+Directory `result` will contain the built distribution which can be served from a web server.
+
+## Questions and Answers
+
+### Why no overlay?
+
+There used to be an
+[overlay](https://nixos.org/manual/nixpkgs/stable/#chap-overlays) for the
+distribution package. But overlays have the disadvantage (in this case) that
+they can be applied to any version of Nixpkgs. But the package, as it is now,
+cannot be built with just any version of Nixpkgs. Updates of Nixpkgs in your
+configuration can break the package and thus your configuration.
+
+For example, this has happened in May 2022 when Node 12 was marked as insecure
+(because it is at the end of its life). But at that point in time, Node 12 was
+still used for building our package. The result was that the package build was
+broken and with it all configurations that use our module.
+
+Since then, we always use a pinned version of Nixpkgs to build the package
+regardless in which configuation the module is used. This has the downside that
+we will miss potential security updates. On the other hand, we only build a
+static website which is very unlikely to have any serious security issues.