Improve Hull and Contour docs

Author: techniq

docs/src/content/components/Contour.md

@@ -2,7 +2,7 @@
 description: Composite mark drawing isolines to delineate regions above and below a particular continuous value. Supports grid data, scattered data with spatial interpolation, and continuous functions.
 category: marks
 layers: [svg]
-related: [Density, Raster, GeoPath]
+related: [Density, Hull, Raster, GeoPath]
 ---
 
 ::tip

docs/src/content/components/Hull.md

@@ -2,9 +2,11 @@
 description: Marking component which encloses a set of data points within a convex boundary to highlight clusters or groupings on a chart.
 category: marks
 layers: [svg, canvas]
-related: []
+related: [Contour, Density, Voronoi]
 ---
 
+The `Hull` mark draws a [convex hull](https://en.wikipedia.org/wiki/Convex_hull) — the tightest convex boundary enclosing a set of points, like stretching a rubber band around pins on a board. It is useful for highlighting clusters or groupings in scatter plots. Supports both Cartesian and geo projections.
+
 ## Usage
 
 :example{ name="scatter" showCode }