Update README.md

Note a default suggected value for cone_weight when cone culling is
used; previously various demos used 0.5, but it's somewhat aggressive
when other forms of culling (esp. occlusion culling are used), so for
now suggest a more conservative default.

Author: zeux

README.md

@@ -419,7 +419,7 @@ size_t meshlet_count = meshopt_buildMeshlets(meshlets.data(), meshlet_vertices.d
     indices.size(), &vertices[0].x, vertices.size(), sizeof(Vertex), max_vertices, max_triangles, cone_weight);
 ```
 
-To generate the meshlet data, `max_vertices` and `max_triangles` need to be set within limits supported by the hardware; for NVidia the values of 64 and 124 are recommended (`max_triangles` must be divisible by 4 so 124 is the value closest to official NVidia's recommended 126). `cone_weight` should be left as 0 if cluster cone culling is not used, and set to a value between 0 and 1 to balance cone culling efficiency with other forms of culling like frustum or occlusion culling.
+To generate the meshlet data, `max_vertices` and `max_triangles` need to be set within limits supported by the hardware; for NVidia the values of 64 and 124 are recommended (`max_triangles` must be divisible by 4 so 124 is the value closest to official NVidia's recommended 126). `cone_weight` should be left as 0 if cluster cone culling is not used, and set to a value between 0 and 1 to balance cone culling efficiency with other forms of culling like frustum or occlusion culling (`0.25` is a reasonable default).
 
 Each resulting meshlet refers to a portion of `meshlet_vertices` and `meshlet_triangles` arrays; the arrays are overallocated for the worst case so it's recommended to trim them before saving them as an asset / uploading them to the GPU: