Update README.md

@@ -91,7 +91,7 @@ ScreenUtil.init(designSize: Size(750, 1334), allowFontScaling: true);
     ScreenUtil().scaleHeight //Ratio of actual height dp to design draft px
     ScreenUtil().scaleHeight //Ratio of actual height dp to design draft px
 
 
     0.2.wp  //0.2 times the screen width
     0.2.wp  //0.2 times the screen width
-    0.5.hp  //50% of screen width
+    0.5.hp  //50% of screen height
 ```
 ```
 
 
 #### Adapt screen size：
 #### Adapt screen size：