message: [Doc] Sku: add sku-selected event document
diff: @@ -110,7 +110,7 @@ Vue.use(Sku);
  | add-cart | Triggered when click cart button | data: Object |
  | buy-clicked | Triggered when click buy button | data: Object |
  | stepper-change | Triggered when stepper value changed | value: number |
  -
  +| sku-selected | Triggered when select sku | { skuValue, selectedSku, selectedSkuComb } |
  ### Methods
  @@ -134,7 +134,9 @@ Use ref to get sku instance and call instance methods
  | sku-actions | Custom button actions |
  #### Data Structure
  +
  #### Sku Data Structure
  +
  ```javascript
  sku: {
  tree: [
  @@ -193,6 +195,7 @@ goods: {
  #### customStepperConfig Data Structure
  +
  ```javascript
  customStepperConfig: {
  // custom quota text
  @@ -218,6 +221,7 @@ customStepperConfig: {
  ```
  #### messageConfig Data Structure
  +
  ```javascript
  messageConfig: {
  // the upload image callback
  