feat: integrate nano-graphrag (#433)

* add nano graph-rag

* ignore entities for relevant context reference

* refactor and add local model as default nano-graphrag

* feat: add kotaemon llm & embedding integration with nanographrag

* fix: add env var for nano GraphRAG

---------

Co-authored-by: Tadashi <tadashi@cinnamon.is>

README.md

@@ -170,7 +170,22 @@ documents and developers who want to build their own RAG pipeline.
 ### Setup GraphRAG
 
 > [!NOTE]
-> Currently GraphRAG feature only works with OpenAI or Ollama API.
+> Official MS GraphRAG indexing only works with OpenAI or Ollama API.
+> We recommend most users to use NanoGraphRAG implementation for straightforward integration with Kotaemon.
+
+<details>
+
+<summary>Setup Nano GRAPHRAG</summary>
+
+- Install nano-GraphRAG: `pip install nano-graphrag`
+- Launch Kotaemon with `USE_NANO_GRAPHRAG=true` environment variable.
+- Set your default LLM & Embedding models in Resources setting and it will be recognized automatically from NanoGraphRAG.
+
+</details>
+
+<details>
+
+<summary>Setup MS GRAPHRAG</summary>
 
 - **Non-Docker Installation**: If you are not using Docker, install GraphRAG with the following command:
 
@@ -181,6 +196,8 @@ documents and developers who want to build their own RAG pipeline.
 - **Setting Up API KEY**: To use the GraphRAG retriever feature, ensure you set the `GRAPHRAG_API_KEY` environment variable. You can do this directly in your environment or by adding it to a `.env` file.
 - **Using Local Models and Custom Settings**: If you want to use GraphRAG with local models (like `Ollama`) or customize the default LLM and other configurations, set the `USE_CUSTOMIZED_GRAPHRAG_SETTING` environment variable to true. Then, adjust your settings in the `settings.yaml.example` file.
 
+</details>
+
 ### Setup Local Models (for local/private RAG)
 
 See [Local model setup](docs/local_model.md).