Update README.md (openai#892)

Author: logankilpatrick

README.md

@@ -94,8 +94,9 @@ stream = client.chat.completions.create(
     messages=[{"role": "user", "content": "Say this is a test"}],
     stream=True,
 )
-for part in stream:
-    print(part.choices[0].delta.content or "")
+for chunk in stream:
+    if chunk.choices[0].delta.content is not None:
+        print(chunk.choices[0].delta.content, end="")
 ```
 
 The async client uses the exact same interface.
@@ -110,8 +111,9 @@ stream = await client.chat.completions.create(
     messages=[{"role": "user", "content": "Say this is a test"}],
     stream=True,
 )
-async for part in stream:
-    print(part.choices[0].delta.content or "")
+async for chunk in stream:
+    if chunk.choices[0].delta.content is not None:
+        print(chunk.choices[0].delta.content, end="")
 ```
 
 ## Module-level client