docs: fix README links

[kidonng]

Description

Fix some links in README which are either broken or redirected.

If anyone has better place to link to, suggestions welcome.

Checklist

• Change is backwards compatible.

• Code formatted with ./format.

• Code tested through nix-shell --pure tests -A run.all.

• Test cases updated/added. See example.

• Commit messages are formatted like

  {component}: {description}
  
  {long description}
  

  See CONTRIBUTING for more information and recent commit messages for examples.

• If this PR adds a new module

  • Added myself as module maintainer. See example.

  • Added myself and the module files to .github/CODEOWNERS.

[sumnerevans]

Not sure about the changes to the Nix and Nixpkgs links either. I don't remember what those links used to have.

[kidonng]

Not sure about the changes to the Nix and Nixpkgs links either. I don't remember what those links used to have.

The last present version of Nix and Nixpkgs pages are found on Wayback Machine. The source files of these pages are removed in NixOS/nixos-homepage#453, as a result of NixOS/nixos-homepage#425.

From my understanding:

• The little info on Nixpkgs page is nuked. The Nixpkgs repository README indeed does not contain all that info, but I wonder if it is that useful for people who aren't familiar with Nix/NixOS.
• The info on Nix page is consolidated into the index page and "Features" page (which is now the "Explore" page). Since NixOS is already pointing to the index page, the "Explore" page seems to be the only destination what Nix can refer to, just my two cents.

[rycee]

I think the links you chose are fine and they certainly are much better than broken links. Much appreciated! Merged to master now.