chore: import upstream snapshot with attribution

docs/developer/add_models.rst

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+Adding Models
+=============
+
+WebLLM allows you to compile custom language models using `MLC-LLM <https://llm.mlc.ai/>`_ and then serve the compiled model through WebLLM.
+
+For instructions on how to compile and add custom models to WebLLM, please refer to the `MLC-LLM documentation <https://llm.mlc.ai/docs/deploy/webllm.html>`_. 

docs/developer/building_from_source.rst

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+Building From Source
+====================
+
+Clone the Repository
+---------------------
+.. code-block:: bash
+
+   git clone https://github.com/mlc-ai/web-llm.git
+   cd web-llm
+
+Install Dependencies
+---------------------
+.. code-block:: bash
+
+   npm install
+
+Build the Project
+-----------------
+.. code-block:: bash
+
+   npm run build
+
+Test Changes
+------------
+
+To test your changes, you can reuse an existing example or create a new example that specifically tests the new functionality you wish to provide.
+
+To test the effects of your code change in an example, inside ``examples/<example>/package.json``, change ``"@mlc-ai/web-llm": "^0.2.xx"`` to ``"@mlc-ai/web-llm": "../.."`` to let it reference your local code. Note that sometimes you may need to switch between ``"file:../.."`` and ``"../.."`` to trigger npm to recognize new changes.
+
+.. code-block:: bash
+
+   cd examples/<example>
+   # Modify package.json as described
+   npm install
+   npm start