Add instructions for running sk_python_flask_chatgpt_plugin locally

[raffertyuy]

Motivation and Context

Current instructions only share how to run using VS Code.

Description

Only updated the sk-python-flask-chatgpt-plugin/README.md file with the new instructions. No code changed.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows SK Contribution Guidelines (https://github.com/microsoft/semantic-kernel-starters/blob/main/CONTRIBUTING.md)
• The code follows the .NET coding conventions (https://learn.microsoft.com/dotnet/csharp/fundamentals/coding-style/coding-conventions) verified with dotnet format
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[raffertyuy]

Cancelling this pull request as I'm adding more contributions.