update readme

Author: hackw

README.md

@@ -34,6 +34,10 @@ The performance of layout and drawing is almost equivalent to a single Flex or S
 performance of constraint calculation is roughly 0.01 milliseconds (layout of general complexity, 20
 child elements). Constraints are only recalculated after they have changed.
 
+A smaller Widget tree leads to less build time and a smaller Element tree. A very flat layout
+structure results in a smaller RenderObject tree and less rendering time. One thing most people tend
+to overlook is that complex nesting can cause build times to sometimes exceed render times.
+
 It is recommended to use ConstraintLayout at the top level. For extremely complex layout(one
 thousand child elements, two thousand constraints), layout and drawing total time within 5
 milliseconds(debug mode on Windows 10，release mode take less time), the frame rate can be easily

README_CN.md

@@ -26,6 +26,9 @@ ConstraintLayout 不会积极支持它。
 
 其中布局和绘制的性能几乎与单一 Flex 或 Stack 相当，约束计算的性能大致为 0.01 毫秒（一般复杂度的布局，20 个子元素）。只有在约束变化后才会重新计算约束。
 
+更小的 Widget 树带来了更少的 build 耗时和更小的 Element 树。非常扁平的布局结构带来了更小的 RenderObject 树和更少的渲染耗时。大多数人容易忽略的事情是复杂嵌套导致
+build 耗时有时甚至超过渲染耗时。
+
 推荐在顶层使用 ConstraintLayout。对于极端复杂的布局（1000 个子元素，2000 个约束），非首帧布局和绘制的总耗时在 5 毫秒内（在 Windows 10
 调试模式下，发布模式耗时更少），理论上首帧优势会更明显。对于常规复杂布局（50 个子元素，100 个约束），帧率可轻松达到 200 fps。