Use `.circleci/Dockerfile` as the default Docker image



I love being able to specify my CI environment as a Docker image. However, currently the process around updating the image is a bit cumbersome.

  • I create a Dockerfile and put it somewhere in the repository (just once, of course)
  • I build the image, push it to docker hub in a public repo
  • I update the .circleci/config.yml file to reflect the new Docker tag

Iā€™d much rather prefer to place a Dockerfile in .circleci as .circleci/Dockerfile and have you take care of the details :wink: Behind the scenes you could build a Docker image and tag it with the SHA of the Dockerfile.