Python: Update README.md

[AndreeaDan27]

prompt_template_config needs PromptTemplateConfig type but req_settings is PromptExecutionSettings type which seems to be accepted better by prompt_execution_settings

Motivation and Context

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄