Add cross-link to gullies tutorial and improve AI image caption

[Valyrian-Code]

Closes #97

Two small improvements to the NumPy integration tutorial:

1. Added a callout note after the streams section pointing to the Earthworks: Gully Modeling tutorial — the two tutorials cover related workflows (stream network extraction + gully modeling).
2. Changed AI edited landscape image caption to AI-enhanced landscape rendering for visual realism (option 3 from the issue).

[Copilot]

Pull request overview

Note

Copilot was unable to run its full agentic suite in this review.

Updates the NumPy/GRASS integration tutorial to add a related reference to gully/stream-network workflows and improve an image caption for clarity/accessibility.

Changes:

• Added a callout linking to the “Earthworks: Gully Modeling” tutorial for stream networks with gullies.
• Improved the final image alt text to be more descriptive.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[Valyrian-Code]

Thanks for the note. All cross-tutorial links in this repo use .qmd paths (e.g., the thematic maps and time series tutorials all reference ../get_started/fast_track.qmd). Quarto resolves these to the correct rendered URLs at build time — the .qmd format is the established pattern here.