Migrating wiki links on Github

[Lassulus]

tracking issue for migration of github links from nixos.wiki to wiki.nixos.org

[astratagem]

Hey, thank you for the pull request. There were a couple issues with suggested replacements that would have ended up as 404 errors:

Update NixOS Wiki link by nixos-wiki · Pull Request #114 · montchr/dotfield

• The official wiki only provides a low-resolution favicon.ico, no favicon.png: [wiki.nixos.org/favicon.ico](https://wiki.nixos.org/favicon.ico)
• The official wiki requires the w/ subpath/prefix before index.php, which affects search URLs and possibly other things: wiki.nixos.org/w/index.php?search=

It might be helpful for future PRs to consider mappings for these particular URLs, as other users likely have configured a similar custom Firefox search engine that needs updating. But I can understand if that's out of scope or more effort than it's worth. The important part is bringing attention to the official wiki, so I still appreciate that 🙂 (and was pleasantly surprised to see this PR just after I had prepared my own fixes committed in astratagem/dotfield@91362ab).