poseidon: enable docker and docker-compose

hosts/poseidon/default.nix

@@ -33,6 +33,10 @@ in
     package = pkgs.unstable.tailscale;
   };
 
+  virtualisation.docker = {
+    enable = true;
+  };
+
   networking.hostName = "poseidon"; # Define your hostname.
   networking.domain = "alarsyo.net";
 
@@ -158,4 +162,8 @@ in
 
   # Takes a long while to build
   documentation.nixos.enable = false;
+
+  environment.systemPackages = with pkgs; [
+    docker-compose
+  ];
 }