docs: add a tutorial for running model locally in a Python extension

docs/tutorials/how_to_run_local_model_in_python_extensions.md

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+# How to Run a Local AI Model in Python Extensions
+
+In the TEN framework, extensions can utilize third-party AI services or run AI models locally to improve performance and reduce costs. This tutorial explains how to run a local AI model in a Python extension and how to interact with it within the extension.
+
+## Step 1: Check Hardware Requirements
+
+Before running an AI model locally, ensure that your hardware meets the necessary requirements. Key components to verify include:
+
+- **CPU/GPU**: Check if the model requires specific processing power.
+- **Memory**: Ensure sufficient memory to load and run the model.
+
+Verify that your system can support the model’s demands to ensure smooth operation.
+
+## Step 2: Install Necessary Software and Dependencies
+
+Once your hardware is ready, install the required software and dependencies. Follow these steps:
+
+1. **Operating System**: Ensure compatibility with your model. Most AI frameworks support Windows, macOS, and Linux, though specific versions may be required.
+2. **Python Version**: Ensure compatibility with the TEN Python runtime and the model.
+3. **Required Libraries**: Install necessary libraries such as:
+
+   - TensorFlow
+   - PyTorch
+   - Numpy
+   - vllm
+
+   You can list the required dependencies in a `requirements.txt` file for easy installation.
+
+4. **Download the Model**: Obtain the local version of the AI model you plan to run.
+
+## Step 3: Implement Your Python Extension
+
+Below is an example of how to implement a basic text generation feature using the `vllm` inference engine in a Python extension.
+
+First, initialize the local model within the extension:
+
+```python
+from ten import (
+    Extension,
+    TenEnv,
+    Cmd,
+    CmdResult,
+)
+from vllm import LLM
+
+class TextGenerationExtension(Extension):
+    def on_init(self, ten_env: TenEnv) -> None:
+        self.llm = LLM(model="<model_path>")
+        ten_env.on_init_done()
+```
+
+Next, implement the `on_cmd` method to handle text generation based on the provided input:
+
+```python
+    def on_cmd(self, ten_env: TenEnv, cmd: Cmd) -> None:
+        prompt = cmd.get_property_string("prompt")
+
+        outputs = self.llm.generate(prompt)
+        generated_text = outputs[0].outputs[0].text
+
+        cmd_result = CmdResult.create(StatusCode.OK)
+        cmd_result.set_property_string("result", generated_text)
+        ten_env.return_result(cmd_result, cmd)
+```
+
+In this code, the `on_cmd` method retrieves the `prompt`, generates text using the model, and returns the generated text as the command result.
+
+You can adapt this approach to implement other functionalities such as image recognition or speech-to-text by processing the relevant input types.
+
+## Step 4: Unload the Model
+
+It’s important to unload the model during extension cleanup to free resources:
+
+```python
+import gc
+import torch
+
+class TextGenerationExtension(Extension):
+    ...
+
+    def on_deinit(self, ten_env: TenEnv) -> None:
+        del self.llm
+        gc.collect()
+        torch.cuda.empty_cache()
+        torch.distributed.destroy_process_group()
+        print("Successfully deleted the LLM pipeline and freed GPU memory!")
+        ten_env.on_deinit_done()
+```
+
+This ensures efficient memory management, especially when working with GPU resources.
+
+## Summary
+
+Running a local model in a TEN Python extension is similar to native Python development. By loading and unloading the model in the appropriate extension lifecycle methods, you can easily integrate local AI models and interact with them effectively.