Update the readme to reflect that the official docker image. Fixes #16

Dockerfile

@@ -1,6 +1,5 @@
-
 FROM    alpine:3.2
-MAINTAINER  Daniel Nephin <dnephin@gmail.com>
+MAINTAINER Kyle Anderson <kwa@yelp.com>
 
 RUN     apk add -U python py-pip
 ADD     requirements.txt /code/requirements.txt

README.rst

@@ -20,10 +20,10 @@ Container
 
 .. code::
 
-    docker pull dnephin/docker-custodian
+    docker pull yelp/docker-custodian
     docker run -ti \
         -v /var/run/docker.sock:/var/run/docker.sock \
-        dnephin/docker-custodian dcgc --help
+        yelp/docker-custodian dcgc --help
 
 Debian/Ubuntu package
 ~~~~~~~~~~~~~~~~~~~~~