Docs: add slot doc for el-upload (#12041)

examples/docs/en-US/upload.md

@@ -419,6 +419,12 @@ disabled | whether to disable upload | boolean | — | false |
 limit | maximum number of uploads allowed | number | — | — |
 on-exceed | hook function when limit is exceeded | function(files, fileList) | — | - |
 
+### Slot
+| Name | Description |
+|------|--------|
+| trigger | content which triggers file dialog |
+| tip | content of tips |
+
 ### Methods
 | Methods Name | Description | Parameters |
 |---------- |-------- |---------- |

examples/docs/es/upload.md

@@ -412,6 +412,12 @@ Puede arrastrar el archivo dentro de un área en especifico para cargar el archi
 | limit            | número máximo de cargas permitidas       | number                             | —                         | —           |
 | on-exceed        | _hook_ lanzado cuando el límite ha sido excedido | function(files, fileList)          | —                         | -           |
 
+### Slot
+| Nombre       | Descripcion                              |
+| ------------ | ---------------------------------------- |
+| trigger | content which triggers file dialog |
+| tip | content of tips |
+
 ### Métodos
 | Nombre del método | Descripción                              | Parametros                |
 | ----------------- | ---------------------------------------- | ------------------------- |

examples/docs/zh-CN/upload.md

@@ -427,6 +427,12 @@
 | limit | 最大允许上传个数 |  number | — | — |
 | on-exceed | 文件超出个数限制时的钩子 | function(files, fileList) | — | - |
 
+### Slot
+| name | 说明 |
+|------|--------|
+| trigger | 触发文件选择框的内容 |
+| tip | 提示说明文字 |
+
 ### Methods
 | 方法名      | 说明          | 参数 |
 |---------- |-------------- | -- |