[docs] Why yolort?

[zhiqwang]

• TorchVision coding style, easy to understand, easy to adapt at will.
• Seamlessly load the official YOLOv5 trained checkpoints, ensuring consistency with the YOLOv5 structure.
• Full unit testing.
• Deployment-friendly, TensorRT / ONNX Runtime / LibTorch / ncnn multi-backend support.

[codecov[bot]]

Codecov Report

Base: 98.58% // Head: 98.58% // No change to project coverage :thumbsup:

Coverage data is based on head (0997758) compared to base (7cdef76). Patch has no changes to coverable lines.

:exclamation: Current head 0997758 differs from pull request most recent head 41d8ca0. Consider uploading reports for the commit 41d8ca0 to get more accurate results

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #459 +/- ## ======================================= Coverage 98.58% 98.58% ======================================= Files 11 11 Lines 778 778 ======================================= Hits 767 767 Misses 11 11 ``` | Flag | Coverage Δ | | |---|---|---| | unittests | `98.58% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zhiqiang+Wang#carryforward-flags-in-the-pull-request-comment) to find out more. Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zhiqiang+Wang). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Zhiqiang+Wang)

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