Added Raindrop.io API

README.md

@@ -660,6 +660,7 @@ API | Description | Auth | HTTPS | CORS |
 | [Pocket](https://getpocket.com/developer/) | Bookmarking service | `OAuth` | Yes | Unknown |
 | [Podio](https://developers.podio.com) | File sharing and productivity | `OAuth` | Yes | Unknown |
 | [PrexView](https://prexview.com) | Data from XML or JSON to PDF, HTML or Image | `apiKey` | Yes | Unknown |
+| [Raindrop.io](https://developer.raindrop.io/) | Bookmarking service | `OAuth` | Yes | Yes |
 | [Restpack](https://restpack.io/) | Provides screenshot, HTML to PDF and content extraction APIs | `apiKey` | Yes | Unknown |
 | [Todoist](https://developer.todoist.com) | Todo Lists | `OAuth` | Yes | Unknown |
 | [Smart Image Enhancement API](https://apilayer.com/marketplace/image_enhancement-api) | Performs image upscaling by adding detail to images through multiple super-resolution algorithms | `apiKey` | Yes | Unknown |