fix missing desktop files for mpv and helix

lib/default.nix

@@ -12,7 +12,10 @@
       configArg ? "-c ",
       excecutable ? "${package}/bin/${name}",
     }:
-    pkgs.writeShellApplication {
+    pkgs.symlinkJoin {
+      inherit name;
+      paths = [
+        (pkgs.writeShellApplication {
           inherit name;
 
           runtimeInputs = [ package ];
@@ -24,5 +27,8 @@
               exec -a "$0" "${excecutable}" ${configArg}"${globalConfig}" "$@"
             fi
           '';
+        })
+        package
+      ];
     };
 }