(docs) update migration

docs/my-website/docs/migration.md

@@ -21,6 +21,12 @@ When we have breaking changes (i.e. going from 1.x.x to 2.x.x), we will document
     max_tokens = litellm.get_max_tokens("gpt-3.5-turbo") # returns an int not a dict 
     assert max_tokens==4097
     ```
+- Streaming - OpenAI Chunks now return `None` for empty stream chunks. This is how to process stream chunks with content
+    ```python
+    response = litellm.completion(model="gpt-3.5-turbo", messages=messages, stream=True)
+    for part in response:
+        print(part.choices[0].delta.content or "")
+    ```
 
 **How can we communicate changes better?**
 Tell us