docs(upload): add file-click index param

document/components/docs/en-US/upload.md

@@ -220,7 +220,7 @@ A function with two parameters: `(file, next)`, the `file` is the original file
 | file-removed | triggers when a file is removed | the file object |
 | file-success | triggers when a file is uploaded successfully | the file object |
 | file-error | triggers when a file is failed to upload | the file object |
-| file-click | triggers when a file is clicked | the file object |
+| file-click | triggers when a file is clicked | the file object. After 1.12.39, added file `index` param |
 | input | triggers when the binding value(file list) changes | the updated value(file list) |
 
 ### Instance methods

document/components/docs/zh-CN/upload.md

@@ -226,7 +226,7 @@
 | file-removed | 文件被删除后触发 | 文件对象 |
 | file-success | 文件上传成功后触发 | 文件对象 |
 | file-error | 文件上传失败后触发 | 文件对象 |
-| file-click | 文件点击后触发 | 文件对象 |
+| file-click | 文件点击后触发 | 文件对象，1.12.39后增加了index文件索引参数 |
 | input | 绑定值（文件列表）改变后触发 | 更新后的绑定值（文件列表） |
 
 ### 实例方法