added comment justifying the detailed computation of the boundingSphere

src/core/BufferGeometry.js

@@ -181,6 +181,9 @@ THREE.BufferGeometry.prototype = {
 
 				box.center( center );
 
+				// hoping to find a boundingSphere with a radius smaller than the
+				//  boundingSphere of the boundingBox:  sqrt(3) smaller in the best case
+
 				var maxRadiusSq = 0;
 
 				for ( var i = 0, il = positions.length; i < il; i += 3 ) {