doc: add joaocgreis as a collaborator

Refer: https://github.com/nodejs/io.js/issues/2102

PR-URL: https://github.com/nodejs/io.js/pull/2208

Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

README.md

@@ -362,6 +362,7 @@ information about the governance of the io.js project, see
 * **Сковорода Никита Андреевич** <chalkerx@gmail.com> ([@ChALkeR](https://github.com/ChALkeR))
 * **Sakthipriyan Vairamani** <thechargingvolcano@gmail.com> ([@thefourtheye](https://github.com/thefourtheye))
 * **Michaël Zasso** <mic.besace@gmail.com> ([@targos](https://github.com/targos))
+* **João Reis** <reis@janeasystems.com> ([@joaocgreis](https://github.com/joaocgreis))
 
 Collaborators & TSC members follow the [COLLABORATOR_GUIDE.md](./COLLABORATOR_GUIDE.md) in
 maintaining the io.js project.