[Doc]: Update the doc of adding new models (#4236)

docs/source/models/adding_model.rst

@@ -95,7 +95,7 @@ This method should load the weights from the HuggingFace's checkpoint file and a
 5. Register your model
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-Finally, include your :code:`*ForCausalLM` class in `vllm/model_executor/models/__init__.py <https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/models/__init__.py>`_ and register it to the :code:`_MODEL_REGISTRY` in `vllm/model_executor/model_loader.py <https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/model_loader.py>`_.
+Finally, register your :code:`*ForCausalLM` class to the :code:`_MODELS` in `vllm/model_executor/models/__init__.py <https://github.com/vllm-project/vllm/blob/main/vllm/model_executor/models/__init__.py>`_.
 
 6. Out-of-Tree Model Integration
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