chore: remove nixpkgs maintainer, update username

Author: RdrSeraphim

CREDITS.md

@@ -8,7 +8,6 @@
 - [Nbc66](https://github.com/Nbc66): added some extra info to the installation guide
 - [OzxyBox](https://github.com/ozxybox): WAD3 parser
 - [Rythyrix](https://github.com/Rythyrix): minor library bugfix
-- [SeraphimRP](https://github.com/SeraphimRP): Nixpkgs maintainer
 - [sour-dani](https://github.com/sour-dani): initial CLI response file implementation
 - [Tholp](https://github.com/Tholp1): major BSP stability improvements
 - [Trico Everfire](https://github.com/Trico-Everfire): open pack files based on Steam game install locations

INSTALL.md

@@ -92,6 +92,6 @@ as I don't use Arch Linux personally and don't know how that system works. (I us
 
 #### NixOS:
 
-VPKEdit is available in NixOS 25.05 and nixpkgs unstable thanks to [@Seraphim Pardee](https://github.com/SeraphimRP).
+VPKEdit is available in NixOS 25.05 and nixpkgs unstable thanks to [@Seraphim Pardee](https://github.com/RdrSeraphim).
 Add it to your system by placing `vpkedit` in the appropriate `environment.systemPackages = with pkgs; [];` section 
 in your Nix configuration. If you want to use it temporarily, run `nix-shell -p vpkedit` then `vpkedit` (for gui) or `vpkeditcli`.