docs: add nuScenes mini setup troubleshooting

[AKilalours]

Summary

This PR adds troubleshooting notes for setting up the nuScenes v1.0-mini dataset with the devkit.

Why

New users can run into path, extraction, or Python environment issues when trying to initialize the devkit with the mini dataset. These notes provide quick checks for common setup problems.

Changes

• Added a table-of-contents entry for mini setup troubleshooting
• Added dataset path checks for v1.0-mini
• Added examples of expected metadata file locations
• Added notes for avoiding nested extraction paths
• Added Python environment verification commands

Testing

• Documentation-only change
• Checked Markdown diff locally

[AKilalours]

Hi maintainers,

I opened this small documentation PR to add troubleshooting notes for v1.0-mini setup, dataset path issues, and Python environment verification.

This is a documentation-only change intended to help new users avoid common setup problems.

Happy to revise if you prefer a different location or wording.