[Docs]: Keep the structure of Chinese document consistent with that of English document (#722)

* Chinese document structure alignment

* fix typos in compatibility.md

docs_zh-CN/0_demo.md

-# 0: 演示
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docs_zh-CN/benchmarks.md

+# 基准测试
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docs_zh-CN/changelog.md

+# 变更日志
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docs_zh-CN/compatibility.md

+# 和过去版本的 MMDetection3D 的兼容性
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docs_zh-CN/datasets/index.rst

+.. toctree::
+   :maxdepth: 2
+
+   scannet_det.md
+   waymo_det.md

docs_zh-CN/datasets/scannet_det.md

+# 3D目标检测Scannet数据集
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docs_zh-CN/datasets/waymo_det.md

+# Waymo数据集
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docs_zh-CN/demo.md

+# 演示
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docs_zh-CN/supported_tasks/index.rst

+.. toctree::
+   :maxdepth: 2
+
+   lidar_det3d.md
+   vision_det3d.md
+   lidar_sem_seg3d.md

docs_zh-CN/supported_tasks/lidar_det3d.md

+# 基于Lidar的3D检测
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docs_zh-CN/supported_tasks/lidar_sem_seg3d.md

+# 基于Lidar的3D语义分割
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docs_zh-CN/supported_tasks/vision_det3d.md

+# 基于视觉的3D检测
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docs_zh-CN/tutorials/waymo.md

-# 教程 6: Waymo 数据集
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