Merge pull request #1236 from tableau/pv/file-doc

Add file type doc

docs/mcd.md

@@ -52,7 +52,7 @@ Each connection attribute is represented by a field element in the XML. The fiel
 | name  | Unique name of the field: used in the platform, connection-normalizer, and connection-builder | No | Names must be unique <br> Name is a Tableau-defined name **OR** prefixed with `v-` | If there is a Tableau-defined name for this attribute, that name must be used. See 'Connection Field Platform Integration' section below. |
 | label | Label that appears on the connection dialog for the field | No | | |
 | placeholder | Placeholder text displayed as a help message when the field has no user input | Yes | | Only applicable for field of type `string`, `textbox` and `file`. |
-| value-type | Dictates the default validation rule and the UI widget | No | Allowed Values: UI Widget Type <br> `string`: text field <br> `textbox`: text area <br> `option`: drop-down <br> `boolean`: checkbox <br> | In the 2020.2 and 2020.3 releases `textbox` is not supported.|
+| value-type | Dictates the default validation rule and the UI widget | No | Allowed Values: UI Widget Type <br> `string`: text field <br> `textbox`: text area <br> `option`: drop-down <br> `boolean`: checkbox <br> `file`: file browser <br> | In the 2020.2 and 2020.3 releases `textbox` is not supported. File type only available on Tableau Desktop and will be disabled on Server and Cloud. |
 | default-value | Default value for the attribute | Yes	| Default values by value-type <br> string: `""` <br> option: first option <br> boolean: `false` <br> file: `""` | |
 | optional | Whether the user must specify a value for the attribute | Yes | Allowed values: `true`, `false`. <br> Default value: `false`. | If a field is in the `advanced` category and is not optional, it must be given a default value. |
 | editable | Whether the user can edit the attribute | Yes | Allowed values: `true`, `false`. <br> Default value: `true`. | When set to `false`, the attribute is not shown in the connection dialog, and its default-value is passed to the ConnectionBuilder(). |