docs(readme): update examples (#893)

README.md

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