doc: Rename to Nixpkgs reference manual and state purpose

For the time being, we're moving towards https://nix.dev/ containing
all tutorials and guides. The Nixpkgs manual is reinforced to be a
_reference_ manual. While it's not just reference for now, that's what
the docs team is working towards.

This commits rewrites the Nixpkgs manual introduction to reflect that
and point to some more useful links. The contribution docs are updated
similarly so it's not missed.

Co-authored-by: Valentin Gagarin <valentin.gagarin@tweag.io>
Co-authored-by: Robert Hensing <roberth@users.noreply.github.com>

4 files changed, 21 insertions, 13 deletions

diff --git a/doc/README.md b/doc/README.md
index 9dee2d30d7305..d441a3b7204a5 100644
--- a/doc/README.md
+++ b/doc/README.md
@@ -1,13 +1,17 @@
-# Contributing to the Nixpkgs manual
+# Contributing to the Nixpkgs reference manual
 
-This directory houses the sources files for the Nixpkgs manual.
+This directory houses the sources files for the Nixpkgs reference manual.
 
-You can find the [rendered documentation for Nixpkgs `unstable` on nixos.org](https://nixos.org/manual/nixpkgs/unstable/).
-The rendering tool is [nixos-render-docs](../pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs), sometimes abbreviated `nrd`.
+Going forward, it should only contain [reference](https://nix.dev/contributing/documentation/diataxis#reference) documentation.
+For tutorials, guides and explanations, contribute to <https://nix.dev/> instead.
+
+For documentation only relevant for contributors, use Markdown files and code comments in the source code.
 
-[Docs for Nixpkgs stable](https://nixos.org/manual/nixpkgs/stable/) are also available.
+Rendered documentation:
+- [Unstable (from master)](https://nixos.org/manual/nixpkgs/unstable/)
+- [Stable (from latest release)](https://nixos.org/manual/nixpkgs/stable/)
 
-If you're only getting started with Nix, go to [nixos.org/learn](https://nixos.org/learn).
+The rendering tool is [nixos-render-docs](../pkgs/tools/nix/nixos-render-docs/src/nixos_render_docs), sometimes abbreviated `nrd`.
 
 ## Contributing to this documentation
 
diff --git a/doc/manual.md.in b/doc/manual.md.in
index 52971ff526c28..642247e166125 100644
--- a/doc/manual.md.in
+++ b/doc/manual.md.in
@@ -1,4 +1,4 @@
-# Nixpkgs Manual {#nixpkgs-manual}
+# Nixpkgs Reference Manual {#nixpkgs-manual}
 ## Version @MANUAL_VERSION@
 
 ```{=include=} chapters
diff --git a/doc/preface.chapter.md b/doc/preface.chapter.md
index aa6acca1217a7..93cd1a00b4f24 100644
--- a/doc/preface.chapter.md
+++ b/doc/preface.chapter.md
@@ -6,11 +6,15 @@ The Nix Packages collection (Nixpkgs) is a set of thousands of packages for the
 Packages are available for several platforms, and can be used with the Nix
 package manager on most GNU/Linux distributions as well as [NixOS](https://nixos.org/nixos).
 
-This manual primarily describes how to write packages for the Nix Packages collection
-(Nixpkgs). Thus it’s mainly for packagers and developers who want to add packages to
-Nixpkgs. If you like to learn more about the Nix package manager and the Nix
-expression language, then you are kindly referred to the [Nix manual](https://nixos.org/nix/manual/).
-The NixOS distribution is documented in the [NixOS manual](https://nixos.org/nixos/manual/).
+This document is the user [_reference_](https://nix.dev/contributing/documentation/diataxis#reference) manual for Nixpkgs.
+It describes entire public interface of Nixpkgs in a concise and orderly manner, and all relevant behaviors, with examples and cross-references.
+
+To discover other kinds of documentation:
+- [nix.dev](https://nix.dev/): Tutorials and guides for getting things done with Nix
+- [NixOS **Option Search**](https://search.nixos.org/options) and reference documentation
+- [Nixpkgs **Package Search**](https://search.nixos.org/packages)
+- [**NixOS** manual](https://nixos.org/manual/nixos/stable/): Reference documentation for the NixOS Linux distribution
+- [`CONTRIBUTING.md`](https://github.com/NixOS/nixpkgs/blob/master/CONTRIBUTING.md): Contributing to Nixpkgs, including this manual
 
 ## Overview of Nixpkgs {#overview-of-nixpkgs}
 
diff --git a/lib/README.md b/lib/README.md
index 220940bc21224..a886cf5bfb555 100644
--- a/lib/README.md
+++ b/lib/README.md
@@ -42,7 +42,7 @@ Reference documentation for library functions is written above each function as
 These comments are processed using [nixdoc](https://github.com/nix-community/nixdoc) and [rendered in the Nixpkgs manual](https://nixos.org/manual/nixpkgs/stable/#chap-functions).
 The nixdoc README describes the [comment format](https://github.com/nix-community/nixdoc#comment-format).
 
-See the [chapter on contributing to the Nixpkgs manual](https://nixos.org/manual/nixpkgs/#chap-contributing) for how to build the manual.
+See [doc/README.md](../doc/README.md) for how to build the manual.
 
 ## Running tests