[Update Documents] update dataset prepare documents about KITTI.

[Raiden-cn]

Motivation

When I used the KITTI dataset, I found that part of the description of the plane information in the data augmentation was missing. The issue is in here

Modification

I update the corresponding docs both english and Chinese.

BC-breaking (Optional)

No breaking changes, just a minor fix.

Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.

This is a new version PR following Contribution Guide, and the previous version is in here.

[Raiden-cn]

Cloud someone review this PR?
I know mmdet3d has been a long time no-update. But as a regular user, I want to be a contributor to mmdet3d.
Thanks!
@ZwwWayne @Tai-Wang @JingweiZhang12 @ZCMax @Xiangxu-0103 @wHao-Wu