doc: add sam-github as collaborator

Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
PR-URL: nodejs#791

Author: sam-github

README.md

@@ -277,6 +277,7 @@ information about the governance of the io.js project, see
 * **Nicu Micleușanu** ([@micnic](https://github.com/micnic)) <micnic90@gmail.com>
 * **Aleksey Smolenchuk** ([@lxe](https://github.com/lxe)) <lxe@lxe.co>
 * **Shigeki Ohtsu** ([@shigeki](https://github.com/shigeki)) <ohtsu@iij.ad.jp>
+* **Sam Roberts** ([@sam-github](https://github.com/sam-github)) <vieuxtech@gmail.com>
 
 Collaborators follow the [COLLABORATOR_GUIDE.md](./COLLABORATOR_GUIDE.md) in
 maintaining the io.js project.