Improve README.md structure and clarity for better onboarding

[evan-william]

This PR proposes an update to the README.md file to improve clarity, consistency, and readability. The goal is to make the introduction and usage instructions easier to understand for new users, while maintaining the original tone and technical accuracy.

What’s Changed:

• Reworded introductory paragraph for smoother flow and better structure.
• Reformatted the “Why Flask?” section for visual clarity and balance.
• Aligned paragraph lengths to improve readability and aesthetic consistency.
• Updated headers and dividers to match the style of the original document.
• Preserved all original links and key information without removing any content.

Motivation:
Flask is often one of the first web frameworks new Python developers try. Improving the readability of the README enhances the first impression and onboarding experience. These small refinements help make Flask even more beginner-friendly without changing its technical content.

Notes:
This PR does not alter any functionality, codebase, or behavior — it is strictly documentation-focused and intended to be helpful for readers.
No issue was opened as this is a minor enhancement (per contributing guidelines).

[davidism]

This change is completely meaningless at best, and feels like an LLM wrote it instead of a human. Don't do that.