doc: add seishun as a collaborator

PR-URL: https://github.com/iojs/io.js/pull/598
Reviewed-By: Brendan Ashworth <brendan.ashworth@me.com>

README.md

@@ -215,6 +215,7 @@ information about the governance of the io.js project, see
 * **Evan Lucas** ([@evanlucas](https://github.com/evanlucas)) <evanlucas@me.com>
 * **Brendan Ashworth** ([@brendanashworth](https://github.com/brendanashworth)) <brendan.ashworth@me.com>
 * **Vladimir Kurchatkin** ([@vkurchatkin](https://github.com/vkurchatkin)) <vladimir.kurchatkin@gmail.com>
+* **Nikolai Vavilov** ([@seishun](https://github.com/seishun)) <vvnicholas@gmail.com>
 
 Collaborators follow the [COLLABORATOR_GUIDE.md](./COLLABORATOR_GUIDE.md) in
 maintaining the io.js project.