[Doc] Add tip on how to use Spec V2 (#15455)

docs/basic_usage/gpt_oss.md

@@ -59,6 +59,24 @@ python -m sglang.launch_server ... --tool-server ip-1:port-1,ip-2:port-2
 ```
 The URLs should be MCP SSE servers that expose server information and well-documented tools. These tools are added to the system prompt so the model can use them.
 
+## Speculative Decoding
+
+SGLang supports speculative decoding for GPT-OSS models using EAGLE3 algorithm. This can significantly improve decoding speed, especially for small batch sizes.
+
+**Usage**:
+Add `--speculative-algorithm EAGLE3` along with the draft model path.
+```bash
+python3 -m sglang.launch_server \
+  --model-path openai/gpt-oss-120b \
+  --speculative-algorithm EAGLE3 \
+  --speculative-draft-model-path lmsys/EAGLE3-gpt-oss-120b-bf16 \
+  --tp 2
+```
+
+```{tip}
+To enable the experimental overlap scheduler for EAGLE3 speculative decoding, set the environment variable `SGLANG_ENABLE_SPEC_V2=1`. This can improve performance by enabling overlap scheduling between draft and verification stages.
+```
+
 ### Quick Demo
 
 ```python