Add teamspeak layer

nixos/layers/teamspeak.nix

+{ pkgs, ... }:
+
+{
+  imports = [
+    # remove once multi-user audio works
+    ./steam.nix
+  ];
+
+  # remove once multi-user audio works
+  users.users.steam = {
+    packages = with pkgs; [
+      teamspeak_client
+    ];
+  };
+
+  users.users.teamspeak = {
+    uid = 1200;
+    isNormalUser = true;
+    packages = with pkgs; [
+      teamspeak_client
+    ];
+    extraGroups = [
+      "audio"
+    ];
+  };
+}
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