add a deprecation notice for trtllm export in doc

Author: Edwardf0t1

docs/source/deployment/1_tensorrt_llm.rst

@@ -2,12 +2,15 @@
 TensorRT-LLM
 ==========================
 
+**Deprecation Notice**: The export_tensorrt_llm_checkpoint API will be deprecated in future releases. Users are encouraged to transition to the :doc:`unified HF export API <3_unified_hf>`, which provides enhanced functionality and flexibility for exporting models to multiple inference frameworks including TensorRT-LLM, vLLM, and SGLang.
+
 .. note::
 
     Please read the `TensorRT-LLM checkpoint workflow <https://github.com/NVIDIA/TensorRT-LLM/blob/main/docs/source/architecture/checkpoint.md>`_
     first before going through this section.
 
 
+
 ModelOpt toolkit supports automatic conversion of ModelOpt exported LLM to the TensorRT-LLM checkpoint and the engines for accelerated inferencing.
 
 This conversion is achieved by: