message: Document switch to explicit flags for docker: cpu / gpu.
diff: ### Running an official image
  -You can run one of the automatic [builds](https://hub.docker.com/r/bvlc/caffe)
  -like this:
  +You can run one of the automatic [builds](https://hub.docker.com/r/bvlc/caffe). E.g. for the CPU version:
  -`docker run -ti bvlc/caffe caffe --version`
  +`docker run -ti bvlc/caffe:cpu caffe --version`
  or for GPU support (You need a CUDA 8.0 capable driver and
  [nvidia-docker](https://github.com/NVIDIA/nvidia-docker)):
  @@ -20,13 +19,13 @@ by root. It also runs by default in a container-private folder.
  You can change this using flags, like user (-u), current directory, and volumes (-w and -v).
  E.g. this behaves like the usual caffe executable:
  -`docker run --rm -u $(id -u):$(id -g) -v $(pwd):$(pwd) -w $(pwd) bvlc/caffe caffe train --solver=example_solver.prototxt`
  +`docker run --rm -u $(id -u):$(id -g) -v $(pwd):$(pwd) -w $(pwd) bvlc/caffe:cpu caffe train --solver=example_solver.prototxt`
  Containers can also be used interactively, specifying e.g. `bash` or `ipython`
  instead of `caffe`.
  ```
  -docker run -ti bvlc/caffe ipython
  +docker run -ti bvlc/caffe:cpu ipython
  import caffe
  ...
  ```
  @@ -39,10 +38,10 @@ utilities can be used directly, e.g. `draw_net.py`, `classify.py`, or `detect.py
  Examples:
  -`docker build -t caffe cpu`
  +`docker build -t caffe:cpu cpu`
  `docker build -t caffe:gpu gpu`
  You can also build Caffe and run the tests in the image:
  -`docker run -ti caffe bash -c "cd /opt/caffe/build; make runtest"`
  +`docker run -ti caffe:cpu bash -c "cd /opt/caffe/build; make runtest"`
  