doc: add rmg to collaborators

PR-URL: https://github.com/nodejs/node/pull/4219
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Calvin Metcalf <calvin.metcalf@gmail.com>

README.md

@@ -410,6 +410,7 @@ information about the governance of the Node.js project, see
 * [petkaantonov](https://github.com/petkaantonov) - **Petka Antonov** <petka_antonov@hotmail.com>
 * [qard](https://github.com/qard) - **Stephen Belanger** <admin@stephenbelanger.com>
 * [rlidwka](https://github.com/rlidwka) - **Alex Kocharin** <alex@kocharin.ru>
+* [rmg](https://github.com/rmg) - **Ryan Graham** <r.m.graham@gmail.com>
 * [robertkowalski](https://github.com/robertkowalski) - **Robert Kowalski** <rok@kowalski.gd>
 * [romankl](https://github.com/romankl) - **Roman Klauke** <romaaan.git@gmail.com>
 * [saghul](https://github.com/saghul) - **Saúl Ibarra Corretgé** <saghul@gmail.com>