docs: clarify how to generate and replay trace files

[Apprentice2907]

Hi 👋

I’ve added a clarification to the README explaining how to correctly generate a JSON trace file using vardbg run before using the replay command to create a video.

The update includes:

• The exact command to generate the trace file
• The correct replay command to produce the video
• Clarification to avoid FileNotFoundError and function lookup errors

This should help new users understand the correct workflow and avoid the issues shown above.

Thanks!