add steam gamescope for remote gaming

nixos/modules/wm/sway.nix

@@ -15,6 +15,7 @@
     evince
     seahorse
     nautilus
+    gamescope
   ];
 
   programs = {
@@ -49,6 +50,19 @@
           binPath = "${pkgs.sway}/bin/sway";
           extraArgs = [ "--unsupported-gpu" ];
         };
+        big_picture = {
+          prettyName = "Steam Big Picture";
+          comment = "Launch in big picture mode within a gamescope container";
+          binPath = "${pkgs.gamescope}/bin/gamescope";
+          extraArgs = [ 
+            "-e"
+            "-W 1920"
+            "-H 1080"
+            "--"
+            "/usr/bin/steam"
+            "-tenfoot"
+          ];
+        };
       };
     };