replace unoffical wiki links with offical ones

pills/01-why-you-should-give-it-a-try.md

@@ -8,7 +8,7 @@ There's a lot of documentation that describes what Nix, [NixOS](https://nixos.or
 
 ## Rationale for this series
 
-The [Nix](https://nixos.org/manual/nix), [Nixpkgs](https://nixos.org/manual/nixpkgs/), and [NixOS](https://nixos.org/manual/nixos/) manuals along with [the wiki](https://nixos.wiki/) are excellent resources for explaining how Nix/NixOS works, how you can use it, and how cool things are being done with it. However, at the beginning you may feel that some of the magic which happens behind the scenes is hard to grasp.
+The [Nix](https://nixos.org/manual/nix), [Nixpkgs](https://nixos.org/manual/nixpkgs/), and [NixOS](https://nixos.org/manual/nixos/) manuals along with [the wiki](https://wiki.nixos.org/) are excellent resources for explaining how Nix/NixOS works, how you can use it, and how cool things are being done with it. However, at the beginning you may feel that some of the magic which happens behind the scenes is hard to grasp.
 
 This series aims to complement the existing explanations from the more formal documents.
 

pills/03-enter-environment.md

@@ -215,7 +215,7 @@ Note: `~/.nix-channels` is not a symlink to the nix store!
 
 To update the channel run `nix-channel --update`. That will download the new Nix expressions (descriptions of the packages), create a new generation of the channels profile and unpack it under `~/.nix-defexpr/channels`.
 
-This is quite similar to `apt-get update`. (See [this table](https://nixos.wiki/wiki/Cheatsheet) for a rough mapping between Ubuntu and NixOS package management.)
+This is quite similar to `apt-get update`. (See [this table](https://wiki.nixos.org/wiki/Cheatsheet) for a rough mapping between Ubuntu and NixOS package management.)
 
 ## Conclusion