docs: extra parameter description. (#524)

* Supplementary parameter description

* Modify English guide.

Author: howareyou2030

README-zh_CN.md

@@ -277,7 +277,7 @@ Also check https://cli.vuejs.org/guide/build-targets.html#library
     * required: `false`
     * default: { lg: 1200, md: 996, sm: 768, xs: 480, xxs: 0 }
 
-    为响应式布局设置断点。
+    为响应式布局设置断点，其中参数代表不同设备的宽度：lg（large），md（medium），sm（small），xs（extra small）。
 
 * **cols**
 
@@ -295,6 +295,13 @@ Also check https://cli.vuejs.org/guide/build-targets.html#library
 
     标识是否使用动态鼠标指针样式。当拖动出现卡顿时，将此值设为 `false`也许可以缓解布局问题。
 
+ * **preventCollision**
+
+    * type: `Boolean`
+    * default: `false`
+
+    值设置为ture时，栅格只能拖动至空白处。
+
 ##### GridItem
 
 * **i**

website/docs/guide/properties.md

@@ -133,7 +133,7 @@ See also [responsiveLayouts](#responsivelayouts), [breakpoints](#breakpoints) an
 * required: `false`
 * default: { lg: 1200, md: 996, sm: 768, xs: 480, xxs: 0 }
 
-Breakpoints defined for responsive layout. Sets widths on wich column number changes
+Breakpoints defined for responsive layout,the parameter represents the width of different devices:lg(large), md(medium), sm(small), xs(extra small). Sets widths on wich column number changes
 
 See also [responsiveLayouts](#responsivelayouts) and [cols](#cols)