The Dockerfile is to simulate the environment that
Travis-CI uses.

To test locally, first create the build container:

    $ docker build -t pbrt:latest .

Then run the image (it executes make by default):

    $ docker run -ti --rm pbrt:latest

To get a copy of the binaries, mount a local directory
into the docker container:

    $ mkdir build
    $ docker run -ti --rm -v $PWD/build:/app/build pbrt:latest

The output will be in $PWD/build.