Fix README

Author: aiguofer

README.rst

@@ -157,7 +157,7 @@ Example
 
     # Save DataFrame to worksheet 'New Test Sheet', create it first if it doesn't exist
     spread.df_to_sheet(df, index=False, sheet='New Test Sheet', start='A2', replace=True)
-    spread.update_cells('A1', 'A1', ['Created by:', spread.email])
+    spread.update_cells('A1', 'B1', ['Created by:', spread.email])
     print(spread)
     # <gspread_pandas.client.Spread - User: '<example_user>@gmail.com', Spread: 'Example Spreadsheet', Sheet: 'New Test Sheet'>