docs: change 'CSV' to 'csv' in python/custreamz/README.md to match ka…

…fka.py (#17041)

This PR corrects a typo in the `python/custreamz/README.md` file by changing the uppercase `'CSV'` to lowercase `'csv'`. This change aligns the documentation with the `message_format` options defined in `python/custreamz/custreamz/kafka.py`, ensuring consistency across the codebase.

Authors:
  - Hirota Akio (https://github.com/a-hirota)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Matthew Murray (https://github.com/Matt711)

URL: #17041

python/custreamz/README.md

@@ -26,7 +26,7 @@ tips_df = consumer.read_gdf(topic="custreamz_tips",
                         partition=0,
                         start=0,
                         end=10000,
-                        message_format="CSV")
+                        message_format="csv")
 
 print(tips_df.head())
 tips_df['tip_percentage'] = tips_df['tip'] / tips_df['total_bill'] * 100