docs: update document

Signed-off-by: ktro2828 <kotaro.uetake@tier4.jp>

Author: ktro2828

docs/tutorials/cli/t4sanity.md

@@ -85,3 +85,33 @@ $ t4sanity <DATA_ROOT> -iw
 | dataset2  |    1    | WARNING |           Category token is empty for surface ann: 0c15d9c143fb2723c16ac7e0c735b0a8            |
 +-----------+---------+---------+------------------------------------------------------------------------------------------------+
 ```
+
+### Dump Results as JSON
+
+To dump results into JSON, use the `-o; --output` option:
+
+```shell
+$ t4sanity <DATA_ROOT> -o results.json
+
+>>>Sanity checking...: 2it [00:00, 21.54it/s]
+...
+```
+
+Then a JSON file named `results.json` will be generated:
+
+```json
+[
+  {
+    "dataset_id": "dataset1",
+    "version": 2,
+    "status": "ERROR",
+    "message": "bbox must be (xmin, ymin, xmax, ymax) and xmin <= xmax && ymin <= ymax: (1532, 198, 1440, 265)"
+  },
+  {
+    "dataset_id": "dataset2",
+    "version": 1,
+    "status": "WARNING",
+    "message": "Category token is empty for surface ann: 0c15d9c143fb2723c16ac7e0c735b0a8"
+  }
+]
+```