How to use ViTDet for customized dataset

Thank you for your good work.

I am new to detectorn2 and I am trying to use detectorn2/ViTDet for the customized datasets, but I do not know where to start.

I read the README: [detectorn2](https://github.com/facebookresearch/detectron2/tree/main/projects/ViTDet), but it has the training and evaluation based on the COCO and LVIS datasets.

I am wondering how I can customize it.

Thank you in advance!

## 📚 Documentation Issue

This issue category is for problems about existing documentation, not for asking how-to questions.

* Provide a link to an existing documentation/comment/tutorial:
https://github.com/facebookresearch/detectron2/tree/main/projects/ViTDet

* How should the above documentation/comment/tutorial improve:
1. Explanation and examples for customized datasets training
2. Introduction to inference testing

Start with the projects/ViTDet README and compare its COCO and LVIS training and evaluation instructions. Document how customized dataset training and inference testing should be explained, using examples that make the updated guidance complete and runnable.

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