[doc] clarify profiling is only for developers (#13554)

Signed-off-by: youkaichao <youkaichao@gmail.com>

docs/source/contributing/profiling/profiling_index.md

 # Profiling vLLM
 
+:::{warning}
+Profiling is only intended for vLLM developers and maintainers to understand the proportion of time spent in different parts of the codebase. **vLLM end-users should never turn on profiling** as it will significantly slow down the inference.
+:::
+
 We support tracing vLLM workers using the `torch.profiler` module. You can enable tracing by setting the `VLLM_TORCH_PROFILER_DIR` environment variable to the directory where you want to save the traces: `VLLM_TORCH_PROFILER_DIR=/mnt/traces/`
 
 The OpenAI server also needs to be started with the `VLLM_TORCH_PROFILER_DIR` environment variable set.
 
 When using `benchmarks/benchmark_serving.py`, you can enable profiling by passing the `--profile` flag.
 
-:::{warning}
-Only enable profiling in a development environment.
-:::
-
 Traces can be visualized using <https://ui.perfetto.dev/>.
 
 :::{tip}