MAINTAINERS: add Brandon Philips

Need to make sure we have a quorum :)

MAINTAINERS

@@ -1,2 +1,3 @@
-Xiang Li <xiang.li@coreos.com> (@xiangli-cmu)
 Blake Mizerany <blake.mizerany@gmail.com> (@bmizerany)
+Brandon Philips <brandon.philips@coreos.com> (@philips)
+Xiang Li <xiang.li@coreos.com> (@xiangli-cmu)