chore: update the docstring for llama2 rmsnorm automatic plugin example (#3512)

Author: bowang007

examples/dynamo/llama2_flashinfer_rmsnorm.py

@@ -1,3 +1,20 @@
+"""
+.._llama2_flashinfer_rmsnorm:
+
+Automatically generate a TensorRT Plugin for RMSNorm module and apply it in Llama2
+===================================================================
+
+This example showcases how to optimize inference for a LLaMA2 model by replacing its RMSNorm layers with FlashInfer's high-performance implementation. It demonstrates the use of Torch-TensorRT's automatic plugin feature, which dynamically generates and integrates custom TensorRT plugins during compilation.
+
+Key features:
+- Leverages automatic plugin registration for FlashInfer RMSNorm ops.
+- Applies a custom TorchDynamo lowering pass to replace standard RMSNorm ops.
+- Compiles the modified model using Torch-TensorRT's Dynamo path.
+- Benchmarks inference performance with and without FlashInfer RMSNorm.
+
+This example illustrates advanced extensibility in Torch-TensorRT through automatic plugin generation and operator lowering customization.
+"""
+
 from typing import Callable, Optional, Sequence, Union
 
 import flashinfer
@@ -86,7 +103,7 @@ def replace_rmsnorm(
                                             args=(node.args[0], 0),
                                         )
                                         b.meta["tensor_meta"] = TensorMetadata(
-                                            shape=torch.Size([]),
+                                            shape=torch.Size([1]),
                                             dtype=torch.int64,
                                             requires_grad=False,
                                             stride=None,