Update README.md

README.md

@@ -38,7 +38,7 @@ The run was preprocessed with [mllam-data-prep](https://github.com/mllam/mllam-d
 ```
 mllam_data_prep data_small/vlasiator_run.yaml
 ```
-This produces training-ready Zarr stores in the `data_small` directory.
+This produces a training-ready Zarr store in the `data_small` directory.
 
 Simple, multiscale, and hierarchical graphs are included already, but can be created using the following commands:
 ```