[docs] note CUDA 8 requirement for Ubuntu 16.04

docs/install_apt.md

@@ -9,14 +9,19 @@ title: Installation: Ubuntu
     sudo apt-get install libprotobuf-dev libleveldb-dev libsnappy-dev libopencv-dev libhdf5-serial-dev protobuf-compiler
     sudo apt-get install --no-install-recommends libboost-all-dev
 
-**CUDA**: Install via the NVIDIA package instead of `apt-get` to be certain of the library and driver versions.
-Install the library and latest driver separately; the driver bundled with the library is usually out-of-date.
+**CUDA**: Install by `apt-get` or the NVIDIA `.run` package.
+The NVIDIA package tends to follow more recent library and driver versions, but the installation is more manual.
+If installing from packages, install the library and latest driver separately; the driver bundled with the library is usually out-of-date.
 This can be skipped for CPU-only installation.
 
 **BLAS**: install ATLAS by `sudo apt-get install libatlas-base-dev` or install OpenBLAS or MKL for better CPU performance.
 
 **Python** (optional): if you use the default Python you will need to `sudo apt-get install` the `python-dev` package to have the Python headers for building the pycaffe interface.
 
+**Compatibility notes, 16.04**
+
+CUDA 8 is required on Ubuntu 16.04.
+
 **Remaining dependencies, 14.04**
 
 Everything is packaged in 14.04.