update readme

Author: fbchen

README.md

@@ -6,8 +6,8 @@ No matter how complex the layout is and how deep the constraints are, it has alm
 performance as Flex and Stack. When facing complex layouts, it provides better performance,
 flexibility, and a very flat code hierarchy than Flex and Stack. Say no to 'nesting hell'.
 
-It is recommended to use ConstraintLayout at the top level. For moderately complex pages, 500 FPS
-performance is promised.
+**It is recommended to use ConstraintLayout at the top level. For moderately complex pages, 500 FPS
+performance is promised.**
 
 Warning:
 For layout performance considerations, constraints are always one-way, and there is no two child