Fix the dockerfile so it can be run locally.  Update README.md.

Change-Id: I47f045e8906a4ad79d6cc08e0d015c6ef318d07e
diff --git a/tools/playground/README.md b/tools/playground/README.md
index 30d1d50..aa0c6af 100644
--- a/tools/playground/README.md
+++ b/tools/playground/README.md
@@ -1,18 +1,12 @@
 # Running the playground compile server locally
 
-Install Docker for Linux:
+Install Docker on Goobuntu:
 
-TODO(sadovsky): These instructions don't seem to work, and furthermore, adding
-docker.list to sources.list.d may pose a security risk.
+  * http://go/installdocker
 
-  $ sudo sh -c "echo deb https://get.docker.io/ubuntu docker main > /etc/apt/sources.list.d/docker.list"
-  $ sudo apt-get update
-  $ sudo apt-get install lxc-docker
-  $ aptitude versions lxc-docker
+Install Docker on OS X:
 
-Or for OS X, from this site:
-
-  https://github.com/boot2docker/osx-installer/releases
+  * https://github.com/boot2docker/osx-installer/releases
 
 Build the playground Docker image (this will take a while...):
 
@@ -20,6 +14,9 @@
 
   $ sudo docker build -t playground $VEYRON_ROOT/veyron/go/src/veyron/tools/playground/builder/.
 
+Note: If you want to ensure an up-to-date version of veyron is installed in the
+Docker image, run the above command with the "--no-cache" flag.
+
 Install the playground binaries:
 
   $ go install veyron/tools/playground/...
diff --git a/tools/playground/builder/Dockerfile b/tools/playground/builder/Dockerfile
index f846ab1..b34ad18 100644
--- a/tools/playground/builder/Dockerfile
+++ b/tools/playground/builder/Dockerfile
@@ -8,10 +8,14 @@
 RUN /usr/local/veyron/bin/veyron profile setup core
 RUN rm /root/.netrc
 
+# Uncomment the following line to use the local copy of vbuild.go.  This is
+# useful when developing and testing local changes to vbuild.go.
+# ADD vbuild.go $VEYRON_ROOT/veyron/go/src/tools/playground/builder
+
 WORKDIR /usr/local/veyron/veyron
-ENV PATH /usr/local/veyron/veyron/go/bin:/usr/local/veyron/veyron/scripts/build:/usr/local/bin:/usr/bin:/bin
-RUN go install veyron/tools/identity veyron/services/mounttable/mounttabled veyron2/vdl/vdl
-RUN go install veyron/tools/playground/builder veyron/tools/playground/compilerd
+ENV PATH /usr/local/veyron/veyron/go/bin:/usr/local/bin:/usr/bin:/bin
+RUN $VEYRON_ROOT/veyron/scripts/build/go install veyron/tools/identity veyron/services/mounttable/mounttabled veyron2/vdl/vdl
+RUN $VEYRON_ROOT/veyron/scripts/build/go install veyron/tools/playground/builder veyron/tools/playground/compilerd
 
 RUN /usr/sbin/useradd -d /home/playground -m playground