Add weights to biomes (#15142)

doc/lua_api.md

@@ -5657,6 +5657,8 @@ Utilities
       bulk_lbms = true,
       -- ABM supports field without_neighbors (5.10.0)
       abm_without_neighbors = true,
+      -- biomes have a weight parameter (5.11.0)
+      biome_weights = true,
   }
   ```
 
@@ -10709,6 +10711,10 @@ performance and computing power the practical limit is much lower.
     -- distribution of the biomes.
     -- Heat and humidity have average values of 50, vary mostly between
     -- 0 and 100 but can exceed these values.
+
+    weight = 1.0,
+    -- Relative weight of the biome in the Voronoi diagram.
+    -- A value of 0 (or less) is ignored and equivalent to 1.0.
 }
 ```