refactored nixos directory & updated README

nixos/sound.nix

@@ -0,0 +1,26 @@
+{ pkgs, ... }:
+
+{
+  # Enable sound with pipewire.
+  sound.enable = true;
+  hardware.pulseaudio.enable = false;
+  security.rtkit.enable = true;
+  services.pipewire = {
+    enable = true;
+    alsa.enable = true;
+    alsa.support32Bit = true;
+    pulse.enable = true;
+    wireplumber.enable = true;
+    # If you want to use JACK applications, uncomment this
+    # jack.enable = true;
+
+    # use the example session manager (no others are packaged yet so this is enabled by default,
+    # no need to redefine it in your config for now)
+    # media-session.enable = true;
+  };
+
+  environment.systemPackages = with pkgs; [
+    pamixer
+    pavucontrol
+  ];
+}