Migrate docs from Sphinx to MkDocs (#18145)

Signed-off-by: Harry Mellor <19981378+hmellor@users.noreply.github.com>

docs/deployment/frameworks/retrieval_augmented_generation.md

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+---
+title: Retrieval-Augmented Generation
+---
+[](){ #deployment-retrieval-augmented-generation }
+
+[Retrieval-augmented generation (RAG)](https://en.wikipedia.org/wiki/Retrieval-augmented_generation) is a technique that enables generative artificial intelligence (Gen AI) models to retrieve and incorporate new information. It modifies interactions with a large language model (LLM) so that the model responds to user queries with reference to a specified set of documents, using this information to supplement information from its pre-existing training data. This allows LLMs to use domain-specific and/or updated information. Use cases include providing chatbot access to internal company data or generating responses based on authoritative sources.
+
+Here are the integrations:
+- vLLM + [langchain](https://github.com/langchain-ai/langchain) + [milvus](https://github.com/milvus-io/milvus)
+- vLLM + [llamaindex](https://github.com/run-llama/llama_index) + [milvus](https://github.com/milvus-io/milvus)
+
+## vLLM + langchain
+
+### Prerequisites
+
+- Setup vLLM and langchain environment
+
+```console
+pip install -U vllm \
+            langchain_milvus langchain_openai \
+            langchain_community beautifulsoup4 \
+            langchain-text-splitters
+```
+
+### Deploy
+
+- Start the vLLM server with the supported embedding model, e.g.
+
+```console
+# Start embedding service (port 8000)
+vllm serve ssmits/Qwen2-7B-Instruct-embed-base
+```
+
+- Start the vLLM server with the supported chat completion model, e.g.
+
+```console
+# Start chat service (port 8001)
+vllm serve qwen/Qwen1.5-0.5B-Chat --port 8001
+```
+
+- Use the script: <gh-file:examples/online_serving/retrieval_augmented_generation_with_langchain.py>
+
+- Run the script
+
+```python
+python retrieval_augmented_generation_with_langchain.py
+```
+
+## vLLM + llamaindex
+
+### Prerequisites
+
+- Setup vLLM and llamaindex environment
+
+```console
+pip install vllm \
+            llama-index llama-index-readers-web \
+            llama-index-llms-openai-like    \
+            llama-index-embeddings-openai-like \
+            llama-index-vector-stores-milvus \
+```
+
+### Deploy
+
+- Start the vLLM server with the supported embedding model, e.g.
+
+```console
+# Start embedding service (port 8000)
+vllm serve ssmits/Qwen2-7B-Instruct-embed-base
+```
+
+- Start the vLLM server with the supported chat completion model, e.g.
+
+```console
+# Start chat service (port 8001)
+vllm serve qwen/Qwen1.5-0.5B-Chat --port 8001
+```
+
+- Use the script: <gh-file:examples/online_serving/retrieval_augmented_generation_with_llamaindex.py>
+
+- Run the script
+
+```python
+python retrieval_augmented_generation_with_llamaindex.py
+```