update planning results notice in readme

Author: ilnehc

README.md

@@ -48,6 +48,8 @@ https://github.com/OpenDriveLab/UniAD/assets/48089846/bcf685e4-2471-450e-8b77-e0
 
 - **`Paper Title Change`**: To avoid confusion with the "goal-point" navigation in Robotics, we change the title from "Goal-oriented" to "Planning-oriented" suggested by Reviewers. Thank you!
 
+- **`Planning Metric`**: Discussion [Ref: https://github.com/OpenDriveLab/UniAD/issues/29]: [Clarification](https://github.com/OpenDriveLab/UniAD/issues/29#issuecomment-1583070151) and [Notice](https://github.com/OpenDriveLab/UniAD/issues/29#issuecomment-1717594344) regarding open-loop planning results comparison.
+
 - **`2023/08/03`** Bugfix [[Commit](https://github.com/OpenDriveLab/UniAD/commit/2e1380143d7af7c93bd67725a11d6960fa4347c6)]: Previously, the visualized planning results were in opposition on the x axis, compared to the ground truth. Now it's fixed.
 
 - **`2023/06/12`** Bugfix [Ref: https://github.com/OpenDriveLab/UniAD/issues/21]: Previously, the performance of the stage1 model (track_map) could not be replicated when trained from scratch, due to mistakenly adding `loss_past_traj` and freezing `img_neck` and `BN`. By removing `loss_past_traj` and unfreezing `img_neck` and `BN` in training, the reported results could be reproduced (AMOTA: 0.393, [stage1_train_log](https://github.com/OpenDriveLab/UniAD/releases/download/v1.0/uniad_reproduce_stage1_gpu16_train.log)).