Add NixOS (again) (#3941)

data/category-dev

@@ -37,6 +37,7 @@ include:kubernetes
 include:microsoft-dev
 include:mongodb
 include:nginx
+include:nixos
 include:openwrt
 include:perl
 include:polymer
@@ -123,7 +124,6 @@ neovim.io
 netfilter.org
 newpipe.net
 nftables.org
-nixos.org
 nodesource.com
 notepad-plus-plus.org
 openresty.org