update README.md

@@ -202,6 +202,9 @@ class _HomePageState extends State<HomePage> {
     0.5.sh  //50% of screen height
     20.setVerticalSpacing  // SizedBox(height: 20 * scaleHeight)
     20.horizontalSpace  // SizedBox(height: 20 * scaleWidth)
+    const RPadding.all(8)   // Padding.all(8.r) - take advantage of const key word
+    REdgeInsts.all(8)       // EdgeInsets.all(8.r)
+    EdgeInsets.only(left:8,right:8).r // EdgeInsets.only(left:8.r,right:8.r).
 ```
 
 #### Adapt screen size：