sai-30624: Add Minimal Usage Example to uftrace README

[sai-30624]

This pull request (ID: sai-30624) adds a “Minimal Usage Example” section to the uftrace README to help new users quickly get started.

What This PR Adds:

• A short example demonstrating how to record and replay a simple command (ls)
• Optional tip for using -a to record function arguments and source lines
• Improves onboarding experience for first-time uftrace users

Why This Change Is Useful:

The current README contains detailed information but lacks a quick-start example.
Adding a minimal usage example lowers the entry barrier, allowing beginners to see uftrace in action immediately.

Author: sai-30624
Email: [email protected]

[namhyung]

Hello, thanks for your contribution!

We already have a animated GIF for quick introduction. Also there's a section "How to use uftrace" to cover the basic usages although it comes a bit later. And I think the simplest command line would be just "uftrace " (without record and replay).