This will build the Docker container on the Circle-CI service. The advantage of Circle-CI over Travis is that Circle-CI will freely work with private GitHub repositories. Only the paid service from Travis will work with private GitHub repositories. Before using this function you need to create an account with Circle-CI, using your GitHub account. If you want Circle-CI to run on a private GitHub repo, make sure you give Circle-CI access to 'all repos' when you log in with your GitHub credentials.
use_circleci(pkg = ".", browse = interactive(), docker_hub = FALSE)defaults to the package in the current working directory
open a browser window to enable Circle-CI builds for the package automatically
should circleci push to Docker Hub after a successful build?