message: docs: add Ubuntu package tracker link in Ubuntu guide
diff: @@ -20,6 +20,10 @@ for CPU-only version, or
  for CUDA version. Note, the cuda version may break if your NVIDIA driver
  and CUDA toolkit are not installed by APT.
  +[Package status of CPU-only version](https://launchpad.net/ubuntu/+source/caffe)
  +
  +[Package status of CUDA version](https://launchpad.net/ubuntu/+source/caffe-contrib)
  +
  **Installing Caffe from source**
  We may install the dependencies by merely one line
  