update docs

docs/user-guide/getting-started/how_to_use.md

@@ -59,4 +59,4 @@ To customize runs, without the need of creating custom config-files, you can ove
 | `MONITOR_METRIC_MODE`   | `str`   | "min" or "max", depending on the `MONITOR_METRIC` used |
 | `REPO_OR_DIR`           | `str`   | GitHub repo with format containing model implementation, e.g. "facebookresearch/dino:main" |
 | `TQDM_REFRESH_RATE`     | `str`   | Determines at which rate (in number of batches) the progress bars get updated. Set it to 0 to disable the progress bar. |
-| `N_DATA_WORKERS`     | `str`   | How many subprocesses to use for the torch dataloaders. |
+| `N_DATA_WORKERS`     | `str`   | How many subprocesses to use for the torch dataloaders. Set to `null` to use the number of cpu cores. |