[Doc] Add sphinx build for vllm-ascend (#55)

### What this PR does / why we need it?

This patch enables the doc build for vllm-ascend

- Add sphinx build for vllm-ascend
- Enable readthedocs for vllm-ascend
- Fix CI:
- exclude vllm-empty/tests/mistral_tool_use to skip `You need to agree
to share your contact information to access this model` which introduce
in
314cfade02
- Install test req to fix
https://github.com/vllm-project/vllm-ascend/actions/runs/13304112758/job/37151690770:
      ```
      vllm-empty/tests/mistral_tool_use/conftest.py:4: in <module>
          import pytest_asyncio
      E   ModuleNotFoundError: No module named 'pytest_asyncio'
      ```
  - exclude docs PR

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
1. test locally:
    ```bash
    # Install dependencies.
    pip install -r requirements-docs.txt
    
    # Build the docs and preview
    make clean; make html; python -m http.server -d build/html/
    ```
    
    Launch browser and open http://localhost:8000/.

2. CI passed with preview:
    https://vllm-ascend--55.org.readthedocs.build/en/55/

Signed-off-by: Yikun Jiang <yikunkero@gmail.com>

docs/source/index.md

@@ -0,0 +1,53 @@
+# Welcome to vLLM Ascend Plugin
+
+:::{figure} ./logos/vllm-ascend-logo-text-light.png
+:align: center
+:alt: vLLM
+:class: no-scaled-link
+:width: 70%
+:::
+
+:::{raw} html
+<p style="text-align:center">
+<strong>vLLM Ascend Plugin
+</strong>
+</p>
+
+<p style="text-align:center">
+<script async defer src="https://buttons.github.io/buttons.js"></script>
+<a class="github-button" href="https://github.com/vllm-project/vllm-ascend" data-show-count="true" data-size="large" aria-label="Star">Star</a>
+<a class="github-button" href="https://github.com/vllm-project/vllm-ascend/subscription" data-icon="octicon-eye" data-size="large" aria-label="Watch">Watch</a>
+<a class="github-button" href="https://github.com/vllm-project/vllm-ascend/fork" data-icon="octicon-repo-forked" data-size="large" aria-label="Fork">Fork</a>
+</p>
+:::
+
+vLLM Ascend plugin (vllm-ascend) is a community maintained hardware plugin for running vLLM on the Ascend NPU.
+
+This plugin is the recommended approach for supporting the Ascend backend within the vLLM community. It adheres to the principles outlined in the [[RFC]: Hardware pluggable](https://github.com/vllm-project/vllm/issues/11162), providing a hardware-pluggable interface that decouples the integration of the Ascend NPU with vLLM.
+
+By using vLLM Ascend plugin, popular open-source models, including Transformer-like, Mixture-of-Expert, Embedding, Multi-modal LLMs can run seamlessly on the Ascend NPU.
+
+## Documentation
+
+% How to start using vLLM on Ascend NPU?
+:::{toctree}
+:caption: Getting Started
+:maxdepth: 1
+quick_start
+installation
+:::
+
+% What does vLLM Ascend Plugin support?
+:::{toctree}
+:caption: Features
+:maxdepth: 1
+features/suppoted_features
+features/supported_models
+:::
+
+% How to contribute to the vLLM project
+:::{toctree}
+:caption: Developer Guide
+:maxdepth: 1
+developer_guide/contributing
+:::