Add README “Story” section for Todo App user flow

[Copilot]

✨ Enhancement

What does this improve?
The README now includes a concrete “Story” narrative, addressing the request to add a story and making the app behavior easier to understand at a glance.

Why is this valuable?
It gives contributors/readers a quick, realistic usage flow (create → complete/filter → return later) and explicitly reinforces localStorage persistence through an example scenario.

Implementation approach:

• Documentation update
  • Added a new ### Story section to README.md.
• Content structure/readability
  • Wrote the story as concise bullet points for fast scanning.
  • Kept language aligned with existing README tone and Todo feature set.
• Session continuity requirement
  • Stored the story-summary fact in memory per issue instruction.

### Story

- Alex starts a new sprint by listing tasks in the Todo App.
- As work finishes, Alex marks items complete and filters between active and completed tasks during daily check-ins.
- At the end of the day, Alex closes the browser and later returns to find every todo still available because the app saves progress with localStorage.