Create 'How to Use' getting-started page

[rdhyee]

Context

Hana's wireframe includes a "How to Use" nav item that doesn't exist on the current site. This should be a simplified entry point for new users.

Possible content

• Quick overview of what you can do (explore samples, filter by source/material, view on globe)
• Step-by-step: open the explorer → search → filter → click a sample → view at source
• Link to tutorials for deeper technical exploration
• Mention browser requirements (modern browser, no installation needed)

Priority

Lower — can be a simple page. The explorer itself should be self-explanatory with good UX.