docs: fix streaming example in README (#16461)

* docs: add messages variable definition in streaming example

- Add missing messages variable in streaming code example
- Makes the example complete and runnable without modifications

* docs: capitalize LiteLLM in streaming section

* docs: add gpt-4o comment

README.md

@@ -132,11 +132,15 @@ print(response)
 
 ## Streaming ([Docs](https://docs.litellm.ai/docs/completion/stream))
 
-liteLLM supports streaming the model response back, pass `stream=True` to get a streaming iterator in response.
+LiteLLM supports streaming the model response back, pass `stream=True` to get a streaming iterator in response.
 Streaming is supported for all models (Bedrock, Huggingface, TogetherAI, Azure, OpenAI, etc.)
 
 ```python
 from litellm import completion
+
+messages = [{"content": "Hello, how are you?", "role": "user"}]
+
+# gpt-4o
 response = completion(model="openai/gpt-4o", messages=messages, stream=True)
 for part in response:
     print(part.choices[0].delta.content or "")