fix typo

docs/datasets/kitti_det.md

@@ -151,13 +151,15 @@ train_pipeline = [
  - `GlobalRotScaleTrans`: rotate input point cloud.
 
 ## Evaluation
+
 An example to evaluate PointPillars with 8 GPUs with kitti metrics is as follows:
 
 ```shell
 bash tools/dist_test.sh configs/pointrcnn/pointrcnn_2x8_kitti-3d-3classes.py work_dirs/pointrcnn_2x8_kitti-3d-3classes/latest.pth 8 --eval bbox
 ```
 
 ## Metrics
+
 KITTI evaluates 3D object detection performance using mean Average Precision (mAP) and Average Orientation Similarity (AOS), Please refer to its [official website](http://www.cvlibs.net/datasets/kitti/eval_3dobject.php) and [original paper](http://www.cvlibs.net/publications/Geiger2012CVPR.pdf) for more details.
 
 We also adopt this approach for evaluation on KITTI. An example of printed evaluation results is as follows: