nixpkgs manual: various improvements in introduction

- rename to preface to be inline with NixOS manual
- refer to other manuals
- use https
- change example channel to 19.09

2 files changed, 13 insertions, 12 deletions

diff --git a/doc/manual.xml b/doc/manual.xml
index de2c70eaf3529..f9a5e56275f9a 100644
--- a/doc/manual.xml
+++ b/doc/manual.xml
@@ -5,7 +5,7 @@
   <subtitle>Version <xi:include href=".version" parse="text" />
   </subtitle>
  </info>
- <xi:include href="introduction.chapter.xml" />
+ <xi:include href="preface.chapter.xml" />
  <part>
   <title>Using Nixpkgs</title>
   <xi:include href="configuration.xml" />
diff --git a/doc/introduction.chapter.md b/doc/preface.chapter.md
index 713c7181a3a03..88ca5e2e3cec5 100644
--- a/doc/introduction.chapter.md
+++ b/doc/preface.chapter.md
@@ -1,44 +1,45 @@
 ---
-title: Introduction
+title: Preface
 author: Frederik Rietdijk
 date: 2015-11-25
 ---
 
-# Introduction
+# Preface
 
 The Nix Packages collection (Nixpkgs) is a set of thousands of packages for the
-[Nix package manager](http://nixos.org/nix/), released under a
+[Nix package manager](https://nixos.org/nix/), released under a
 [permissive MIT/X11 license](https://github.com/NixOS/nixpkgs/blob/master/COPYING).
 Packages are available for several platforms, and can be used with the Nix
-package manager on most GNU/Linux distributions as well as NixOS.
+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](http://nixos.org/nix/manual/).
+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/).
 
 ## Overview of Nixpkgs
 
 Nix expressions describe how to build packages from source and are collected in
 the [nixpkgs repository](https://github.com/NixOS/nixpkgs). Also included in the
 collection are Nix expressions for
-[NixOS modules](http://nixos.org/nixos/manual/index.html#sec-writing-modules).
+[NixOS modules](https://nixos.org/nixos/manual/index.html#sec-writing-modules).
 With these expressions the Nix package manager can build binary packages.
 
 Packages, including the Nix packages collection, are distributed through
-[channels](http://nixos.org/nix/manual/#sec-channels). The collection is
+[channels](https://nixos.org/nix/manual/#sec-channels). The collection is
 distributed for users of Nix on non-NixOS distributions through the channel
 `nixpkgs`. Users of NixOS generally use one of the `nixos-*` channels, e.g.
-`nixos-16.03`, which includes all packages and modules for the stable NixOS
-16.03. Stable NixOS releases are generally only given
+`nixos-19.09`, which includes all packages and modules for the stable NixOS
+19.09. Stable NixOS releases are generally only given
 security updates. More up to date packages and modules are available via the
 `nixos-unstable` channel.
 
 Both `nixos-unstable` and `nixpkgs` follow the `master` branch of the Nixpkgs
 repository, although both do lag the `master` branch by generally
-[a couple of days](http://howoldis.herokuapp.com/). Updates to a channel are
+[a couple of days](https://howoldis.herokuapp.com/). Updates to a channel are
 distributed as soon as all tests for that channel pass, e.g.
-[this table](http://hydra.nixos.org/job/nixpkgs/trunk/unstable#tabs-constituents)
+[this table](https://hydra.nixos.org/job/nixpkgs/trunk/unstable#tabs-constituents)
 shows the status of tests for the `nixpkgs` channel.
 
 The tests are conducted by a cluster called [Hydra](http://nixos.org/hydra/),