Added a missing space in app.h

When the user runs "--help", they see the non-existent word
"compressingnew". This is because of a missing space, which
is now added, resulting in "compressing new".

util/app.h

@@ -199,7 +199,7 @@ struct LoaderArgs : public ArgsBase<LoaderArgs> {
     visitor(weights, "weights", Path(),
             "Path name of model weights (.sbs) file. Only required if "
             "compressed_weights file is not present and needs to be "
-            "regenerated. This parameter is only required for compressing"
+            "regenerated. This parameter is only required for compressing "
             "new model weight exports, otherwise it is not needed.");
   }
 };