[Doc] Move waymo doc and create datasets doc (#689)

* Create index.rst

* Create waymo_det.md

* Add waymo doc link

* Delete waymo.md

* Update index.rst

* Update index.rst

docs/datasets/index.rst

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

docs/tutorials/waymo.md → docs/datasets/waymo_det.md

-# Tutorial 6: Waymo Dataset
+# Waymo Dataset
 
 This page provides specific tutorials about the usage of MMDetection3D for waymo dataset.
 

docs/index.rst

@@ -23,6 +23,12 @@ Welcome to MMDetection3D's documentation!
 
    supported_tasks/index.rst
 
+.. toctree::
+   :maxdepth: 2
+   :caption: Datasets
+
+   datasets/index.rst
+
 .. toctree::
    :maxdepth: 2
    :caption: Tutorials

docs/tutorials/index.rst

@@ -6,4 +6,3 @@
    data_pipeline.md
    customize_models.md
    customize_runtime.md
-   waymo.md