Update README with land.pmtiles attribution

README.md

@@ -33,6 +33,7 @@ exaggeration controls.
 
 - `gebco_2026_terrain_rgb.pmtiles`: GEBCO 2026 global bathymetry in **Terrain-RGB** format (6.0 GB).
 - `gebco-2025-rawrgb-z0-6-webp.pmtiles`: GEBCO 2025 low-resolution overview in **Raw RGB** (WebP format, 204 MB).
+- `land.pmtiles`: Land polygons derived from **Natural Earth** data (16.9 MB).
 
 ## Compute & Provenance
 
@@ -65,4 +66,10 @@ Two GEBCO grid releases are used in this dataset:
 
 The GEBCO Grid is placed in the public domain and may be used free of charge.
 This dataset does not claim any official status and is not endorsed by GEBCO,
-the IHO, or the IOC. For more information visit [gebco.net](https://www.gebco.net/).
+the IHO, or the IOC. For more information visit [gebco.net](https://www.gebco.net/).
+
+### Natural Earth Data
+
+Land polygons are derived from [Natural Earth](https://www.naturalearthdata.com/).
+"Made with Natural Earth. Free vector and raster map data @ naturalearthdata.com."
+Natural Earth data is public domain.