Use jessie-backports when installing jdk-8.

Otherwise gets an "unmet depenedencies" error.

Change-Id: I629cc3d8dda73fbd414604970e0f6c213011008c
diff --git a/README.md b/README.md
index d6fa0b6..3b745aa 100644
--- a/README.md
+++ b/README.md
@@ -30,6 +30,7 @@
 	 and put them in `/etc/apt/sources.list.d/`.
   1. Install the required packages:
 ```console
+apt-get install -t jessie-backports openjdk-8-jdk
 apt-get install python libpython-dev bazel ruby clang-format-3.5 clang-3.6 gfortran libblas-dev liblapack-dev python-scipy python-matplotlib
 ```
   2. Allow Bazel's sandboxing to work: