update readme

README.md

@@ -1,9 +1,9 @@
 # flutter_gifimage
 
 We should know that in order to achieve Gif in flutter, we can use Image, but we have no way to manipulate Gif, for example: change its speed, control it has been playing in a frame,
- in which frame range loop. These problems can be solved by this control.
+ in which frame range loop. These problems can be solved by this widget,it also help you contain gif cache,avoid load frame every time.
 
-* Usage(Simple)
+# Usage(Simple)
 
  ```dart
      controller4= GifController(vsync: this);