优化 permission 相关的注释

yudao-ui-admin/src/directive/index.js

@@ -5,6 +5,7 @@ import dialogDragWidth from './dialog/dragWidth'
 import dialogDragHeight from './dialog/dragHeight'
 import clipboard from './module/clipboard'
 
+// Vue：自定义指令：https://v2.cn.vuejs.org/v2/guide/custom-directive.html
 const install = function(Vue) {
   Vue.directive('hasRole', hasRole)
   Vue.directive('hasPermi', hasPermi)