Update README.md, adding bboxSize to toc

Author: DanielJDufour

README.md

@@ -11,6 +11,7 @@ Bounding boxes, or rectangular extents, are represented as an array of 4 numbers
 - [bboxArea](#bboxArea)
 - [bboxArray](#bboxArray)
 - [bboxPoint](#bboxPoint)
+- [bboxSize](#bboxSize)
 - [booleanContains](#booleanContains)
 - [booleanContainsPoint](#booleanContainsPoint)
 - [booleanIntersects](#booleanIntersects)
@@ -339,4 +340,4 @@ preciseDensePolygon(bbox, { density: [359, 179] }); // add 359 points to top and
 
 preciseDivide([0, 9, 50, 200], [3, 4], { ellipsis: true })
 ["0", "2.25", "16.666...", "50"]
-```
+```