[UX] improve profiler error message (#31125)

Signed-off-by: Boyuan Feng <boyuan@meta.com>

vllm/v1/worker/gpu_worker.py

@@ -634,7 +634,12 @@ class Worker(WorkerBase):
 
     def profile(self, is_start: bool = True):
         if self.profiler is None:
-            raise RuntimeError("Profiling is not enabled.")
+            raise RuntimeError(
+                "Profiling is not enabled. Please set --profiler-config to enable "
+                "profiling. Example: "
+                "'--profiler-config.profiler=torch --profiler-config.torch_profiler_dir"
+                "=YOUR_DIR_PATH_TO_DUMP_TRACE'"
+            )
         if is_start:
             self.profiler.start()
         else: