zeroad: Add myself as a maintainer

pkgs/games/0ad/data.nix

···
     description = "A free, open-source game of ancient warfare -- data files";
     homepage = "https://play0ad.com/";
     license = licenses.cc-by-sa-30;
+    maintainers = with maintainers; [ chvp ];
     platforms = platforms.linux;
     hydraPlatforms = [];
   };

pkgs/games/0ad/game.nix

···
       gpl2 lgpl21 mit cc-by-sa-30
       licenses.zlib # otherwise masked by pkgs.zlib
     ];
+    maintainers = with maintainers; [ chvp ];
     platforms = subtractLists platforms.i686 platforms.linux;
   };
 }