[Doc]: Add developer guide docs for OpenCompass evaluation

[Yikun]

📚 The doc issue

Please add:
[1] vllm-ascend/docs/source/developer_guide/evaluation/index.md
[2] vllm-ascend/docs/source/developer_guide/evaluation/using_opencompass.md

Suggest a potential alternative/fix

No response

[zhangxinyuehfad]

📚 The doc issue

Please add: [1] vllm-ascend/docs/source/developer_guide/evaluation/index.md [2] vllm-ascend/docs/source/developer_guide/evaluation/using_opencompass.md

Suggest a potential alternative/fix

No response

added : PR368

[Yikun]

Closed by: #368