Add openjdk-7-source to the install guide for Ubuntu
Add openjdk-7-source to the install guide for Ubuntu

This is a dependency due to issue #69.

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MOS_MIGRATED_REVID=96751552

bazelbuild/bazel-website,davidzchen/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website,bazelbuild/bazel-website,davidzchen/bazel-website