document using nixos-anywhere without flakes and disko

Author: Mic92

docs/howtos/use-without-flakes.md

@@ -3,6 +3,8 @@
 While `nixos-anywhere` is designed to work optimally with Nix Flakes, it also
 supports the traditional approach without flakes. This document outlines how to
 use `nixos-anywhere` without relying on flakes.
+You will need to [import the disko nixos module](https://github.com/nix-community/disko/blob/master/docs/HowTo.md#installing-nixos-module) in your NixOS configuration
+and define disko devices as described in the [examples](https://github.com/nix-community/disko/tree/master/example).
 
 ## Generate Required Store Paths