Updated Filer Server API (markdown)

Filer-Server-API.md

@@ -33,6 +33,7 @@ You can append to any HTTP API with &pretty=y to see a formatted json output.
 | mode | file mode | 0660 |
 | op | file operation, currently only support "append" | empty |
 | header: `Content-Type` | used for auto compression | empty |
+| header: `Content-Disposition` | used as response content-disposition | empty |
 | prefixed header: `Seaweed-` | example: `Seaweed-name1: value1`. Returned as `Seaweed-Name1: value1` in GET/HEAD response header. | empty |
 ### notice
 * It is recommended to add retries when writing to Filer.