[Docs] Clean up speculators docs (#34065)

Signed-off-by: Kyle Sayers <kylesayrs@gmail.com>

docs/features/speculative_decoding/draft_model.md

@@ -0,0 +1,80 @@
+# Draft Models
+
+The following code configures vLLM in an offline mode to use speculative decoding with a draft model, speculating 5 tokens at a time.
+
+```python
+from vllm import LLM, SamplingParams
+
+prompts = ["The future of AI is"]
+sampling_params = SamplingParams(temperature=0.8, top_p=0.95)
+
+llm = LLM(
+    model="Qwen/Qwen3-8B",
+    tensor_parallel_size=1,
+    speculative_config={
+        "model": "Qwen/Qwen3-0.6B",
+        "num_speculative_tokens": 5,
+        "method": "draft_model",
+    },
+)
+outputs = llm.generate(prompts, sampling_params)
+
+for output in outputs:
+    prompt = output.prompt
+    generated_text = output.outputs[0].text
+    print(f"Prompt: {prompt!r}, Generated text: {generated_text!r}")
+```
+
+To perform the equivalent launch in online mode, use the following server-side code:
+
+```bash
+vllm serve Qwen/Qwen3-4B-Thinking-2507 \
+    --host 0.0.0.0 \
+    --port 8000 \
+    --seed 42 \
+    -tp 1 \
+    --max_model_len 2048 \
+    --gpu_memory_utilization 0.8 \
+    --speculative_config '{"model": "Qwen/Qwen3-0.6B", "num_speculative_tokens": 5, "method": "draft_model"}'
+```
+
+The code used to request as completions as a client remains unchanged:
+
+??? code
+
+    ```python
+    from openai import OpenAI
+
+    # Modify OpenAI's API key and API base to use vLLM's API server.
+    openai_api_key = "EMPTY"
+    openai_api_base = "http://localhost:8000/v1"
+
+    client = OpenAI(
+        # defaults to os.environ.get("OPENAI_API_KEY")
+        api_key=openai_api_key,
+        base_url=openai_api_base,
+    )
+
+    models = client.models.list()
+    model = models.data[0].id
+
+    # Completion API
+    stream = False
+    completion = client.completions.create(
+        model=model,
+        prompt="The future of AI is",
+        echo=False,
+        n=1,
+        stream=stream,
+    )
+
+    print("Completion results:")
+    if stream:
+        for c in completion:
+            print(c)
+    else:
+        print(completion)
+    ```
+
+!!! warning
+    Note: Please use `--speculative_config` to set all configurations related to speculative decoding. The previous method of specifying the model through `--speculative_model` and adding related parameters (e.g., `--num_speculative_tokens`) separately has been deprecated.