Prerequisites for NixOS

Hi there,

When I installed DMS for NixOS on my machine, I installed it using the flake method as that is what my system is currently uses. In the documentation under _DankMaterialShell (dms) -> Installation_ there is a _Dependencies_ section that says that Niri (or any compositor) was optional and Quickshell was required. This confused me when I installed the flake without niri and the system didn't boot up without a compositor.

IMO I think that the `Flake (NixOS/home-manager)` page should have it's own Prerequisite/Dependencies section at the top to make it clear that they differ from the original `DankMaterialShell (dms) -> Installation` page `Dependencies`. It seems that the flake setup doesn't actually require Quickshell but does require Niri to be installed separately.

Start with the `Flake (NixOS/home-manager)` page and compare its prerequisites with the `DankMaterialShell (dms) -> Installation` page and its `Dependencies` section. Confirm which dependencies apply to the flake setup, then add a clearly placed prerequisites section that explains the compositor and Quickshell requirements; the documentation is done when the two installation paths are no longer ambiguous.

Written by the indexing model from the issue text.