Update 'README.md'

README.md

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 # llama_index
 
-LlamaIndex (GPT Index) is a project that provides a central interface to connect your LLM's with external data.
+LlamaIndex (GPT Index) is a project that provides a central interface to connect your LLM's with external data.
+
+文档：
+
+https://gpt-index.readthedocs.io/en/latest/
+
+
+To build a simple vector store index:
+
+```
+import os
+os.environ["OPENAI_API_KEY"] = 'YOUR_OPENAI_API_KEY'
+
+from llama_index import GPTSimpleVectorIndex, SimpleDirectoryReader
+documents = SimpleDirectoryReader('data').load_data()
+index = GPTSimpleVectorIndex(documents)
+```
+
+To save to and load from disk:
+
+```
+# save to disk
+index.save_to_disk('index.json')
+# load from disk
+index = GPTSimpleVectorIndex.load_from_disk('index.json')
+```
+
+To query:
+
+```
+index.query("<question_text>?")
+```