docs: add required `LLMConfig` for Azure OpenAI

[PrettyWood]

fix #557

[!IMPORTANT] Updates README.md to include LLMConfig setup for Azure OpenAI integration.

• Documentation:
  • Adds import for LLMConfig in README.md for Azure OpenAI setup.
  • Introduces LLMConfig creation with Azure model names in README.md.
  • Updates Graphiti initialization example to include llm_config for OpenAIClient and OpenAIRerankerClient.

^{This description was created by for 543c07050083b85974ee208d3318e4a196e12589. You can customize this summary. It will automatically update as commits are pushed.}

[danielchalef]

All contributors have signed the CLA ✍️ ✅
_{Posted by the CLA Assistant Lite bot.}

[PrettyWood]

I have read the CLA Document and I hereby sign the CLA