adds correio public api doc (#2668)

README.md

@@ -1429,6 +1429,7 @@ API | Description | Auth | HTTPS | CORS |
 ### Tracking
 API | Description | Auth | HTTPS | CORS |
 |---|---|---|---|---|
+| [Correios](https://cws.correios.com.br/ajuda) | Integration to provide information and prepare shipments using Correio's services | `apiKey` | Yes | Unknown |
 | [Pixela](https://pixe.la) | API for recording and tracking habits or effort, routines | `X-Mashape-Key` | Yes | Yes |
 | [Postmon](http://postmon.com.br) | An API to query Brazilian ZIP codes and orders easily, quickly and free | No | No | Unknown |
 | [PostNord](https://developer.postnord.com/api) | Provides information about parcels in transport for Sweden and Denmark | `apiKey` | No | Unknown |