add RectangleAttach

doc/source/handycontrol/attach/rectangleAttach/index.md

@@ -0,0 +1,19 @@
+---
+title: RectangleAttach Rectangle专用
+---
+
+# 属性
+
+| 名称 | 用途 |
+|-|-|
+| CornerRadius | 设置Rectangle圆角值 |
+
+# 使用案例
+
+## CornerRadius 设置Rectangle圆角值
+
+```xml
+<Rectangle Fill="Red" Width="100" Height="60" hc:RectangleAttach.Circular="True"/>
+```
+
+![RectangleAttach.CornerRadius](https://raw.githubusercontent.com/HandyOrg/HandyOrgResource/master/HandyControl/Doc/attach/RectangleAttach.CornerRadius.png)