[Docs] refactor Contribution Guide

docs/references/contribution_guide.md

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+# Contribution Guide
+
+Welcome to **SGLang**! We appreciate your interest in contributing. This guide provides a concise overview of how to set up your environment, run tests, build documentation, and open a Pull Request (PR). Whether you’re fixing a small bug or developing a major feature, we encourage following these steps for a smooth contribution process.
+
+---
+
+## 1. Setting Up & Building from Source
+
+### 1.1 Fork and Clone the Repository
+
+> **Note**: SGLang does **not** accept PRs on the main repo. Please fork the repository under your GitHub account, then clone your fork locally.
+
+```bash
+git clone https://github.com/<your_user_name>/sglang.git
+cd sglang
+```
+
+### 1.2 Install Dependencies & Build
+
+Refer to our [Install SGLang](https://sgl-project.github.io/start/install.html) documentation for more details on setting up the necessary dependencies.
+
+Before installing packages like FlashInfer, ensure your local PyTorch and CUDA versions match:
+
+```bash
+python -c "import torch; print('PyTorch Version:', torch.__version__); print('CUDA Version:', torch.version.cuda)"
+nvidia-smi
+```
+
+Based on this information, choose the correct FlashInfer package (or any other CUDA-dependent library).
+Below is an example assuming you have **PyTorch 2.4** with **CUDA 12.4**:
+
+```bash
+# Example: Installing FlashInfer (Pick the right version for your CUDA/PyTorch)
+pip install --upgrade pip
+pip install -e "python[all]" --find-links https://flashinfer.ai/whl/cu124/torch2.4/flashinfer/
+
+# Now install the latest SGLang
+cd sglang/python
+pip install .
+```
+---
+
+## 2. Code Formatting with Pre-Commit
+
+We use [pre-commit](https://pre-commit.com/) to maintain consistent code style checks. Before pushing your changes, please run:
+
+```bash
+pip3 install pre-commit
+cd sglang
+pre-commit run --all-files
+```
+
+- **`pre-commit run --all-files`** manually runs all configured checks, applying fixes if possible.
+- If it fails the first time, re-run it to ensure lint errors are fully resolved.
+- Make sure your code passes all checks **before** creating a Pull Request.
+- **Do not commit** directly to the `main` branch. Always create a new branch (e.g., `feature/my-new-feature`), push your changes, and open a PR from that branch.
+
+---
+
+## 3. Writing Documentation & Running Docs CI
+
+Most documentation files are located under the `docs/` folder. We prefer **Jupyter Notebooks** over Markdown so that all examples can be executed and validated by our docs CI pipeline.
+
+### 3.1 Docs Workflow
+
+```bash
+# 1) Compile all Jupyter notebooks
+make compile
+
+# 2) Generate static HTML
+make html
+
+# 3) Preview documentation locally
+bash serve.sh
+# Open your browser at the displayed port to view the docs
+
+# 4) Clean notebook outputs
+pip install nbstripout
+find . -name '*.ipynb' -exec nbstripout {} \;
+# nbstripout removes notebook outputs so your PR stays clean
+
+# 5) Pre-commit checks and create a PR
+pre-commit run --all-files
+# After these checks pass, push your changes and open a PR on your branch
+```
+
+- Add or update your Jupyter notebooks in the appropriate subdirectories under `docs/`.
+- If you add new files, remember to update `index.rst` (or relevant `.rst` files) accordingly.
+
+- For tasks that require a running SGLang backend, you might launch a server process or an engine instance. Once you finish testing or using it, **remember to shut it down**. Refer to:
+
+1. [OpenAI API Completions Docs](https://sgl-project.github.io/backend/openai_api_completions.html)
+     ```python
+     from sglang.backend.utils import terminate_process
+     # ...
+     terminate_process(server_process)
+     ```
+
+2. [Offline Engine API Docs](https://sgl-project.github.io/backend/offline_engine_api.html)
+     ```python
+     llm.shutdown()
+     ```
+
+
+---
+
+## 4. Running Unit Tests & Adding to CI
+
+SGLang uses Python’s built-in [unittest](https://docs.python.org/3/library/unittest.html) framework. You can run tests either individually or in suites.
+
+### 4.1 Test Backend Runtime
+
+```bash
+cd sglang/test/srt
+
+# Run a single file
+python3 test_srt_endpoint.py
+
+# Run a single test
+python3 -m unittest test_srt_endpoint.TestSRTEndpoint.test_simple_decode
+
+# Run a suite with multiple files
+python3 run_suite.py --suite minimal
+```
+
+### 4.2 Test Frontend Language
+
+```bash
+cd sglang/test/lang
+export OPENAI_API_KEY=sk-*****
+
+# Run a single file
+python3 test_openai_backend.py
+
+# Run a single test
+python3 -m unittest test_openai_backend.TestOpenAIBackend.test_few_shot_qa
+
+# Run a suite with multiple files
+python3 run_suite.py --suite minimal
+```
+
+### 4.3 Adding or Updating Tests in CI
+
+- Create new test files under `test/srt` or `test/lang` depending on the type of test.
+- Ensure they are referenced in the respective `run_suite.py` (e.g., `test/srt/run_suite.py` or `test/lang/run_suite.py`) so they’re picked up in CI.
+- In CI, all tests run automatically. You may modify the workflows in [`.github/workflows/`](https://github.com/sgl-project/sglang/tree/main/.github/workflows) to add custom test groups or extra checks.
+
+### 4.4 Writing Elegant Test Cases
+
+- Examine existing tests in [sglang/test](https://github.com/sgl-project/sglang/tree/main/test) for practical examples.
+- Keep each test function focused on a single scenario or piece of functionality.
+- Give tests descriptive names reflecting their purpose.
+- Use robust assertions (e.g., assert, unittest methods) to validate outcomes.
+- Clean up resources to avoid side effects and preserve test independence.
+
+---
+
+
+## 5. Tips for Newcomers
+
+If you want to contribute but don’t have a specific idea in mind, pick issues labeled [“good first issue” or “help wanted”](https://github.com/sgl-project/sglang/issues?q=is%3Aissue+label%3A%22good+first+issue%22%2C%22help+wanted%22). These tasks typically have lower complexity and provide an excellent introduction to the codebase. Also Check out this [code walk-through](https://github.com/zhaochenyang20/Awesome-ML-SYS-Tutorial/tree/main/sglang/code-walk-through) for a deeper look into SGLang’s workflow.
+
+If you have any questions or want to start a discussion, please feel free to ask in our [Slack channel](https://join.slack.com/t/sgl-fru7574/shared_invite/zt-2um0ad92q-LkU19KQTxCGzlCgRiOiQEw).
+
+Thank you for your interest in SGLang—**happy coding**!