fix: change import in usage

README.md

@@ -17,7 +17,7 @@ This command will install langchain_g4f.
 Here is an example of how to use langchain_g4f
 
 ```python
-from g4f import Provider, Model
+from g4f import Provider, models
 from langchain.llms.base import LLM
 
 from langchain_g4f import G4FLLM
@@ -25,15 +25,15 @@ from langchain_g4f import G4FLLM
 
 def main():
     llm: LLM = G4FLLM(
-        model=Model.gpt_35_turbo,
+        model=models.gpt_35_turbo,
         provider=Provider.Aichat,
     )
 
-    res = llm('hello')
+    res = llm("hello")
     print(res)  # Hello! How can I assist you today?
 
 
-if __name__ == '__main__':
+if __name__ == "__main__":
     main()
 ```