This pull request contains two commits:

Update the Dockerfile with some best practices and corrections:

• Install go dependencies separately from building nom. This allows the
  container engine to cache the dependencies, saving time on future
  builds.

• Use a multi-stage build so that the final image does not contain our
  build dependencies, source code, compiled code, etc.

• Install docker-config.yml as described in the README. Previously, this
  file was not installed in the image.

• Install the nano editor so that using E in the
  item list will allow someone to customize the configuration.

• Configure nom as the ENTRYPOINT, so that when passing in custom flags
  it's not necessary to write nom twice. That is, instead of:

  docker run -it --rm nom nom -c /a/different/path
  

  You can write:

  docker run -it --rm nom -c /a/different/path
  

Update the README

This commit makes a number of small edits to the README:

• Run README through dpring fmt --stdin .md
• Add an additional install example
• Mention the -c alias for --config-path
• Minor changes to capitalization and phrasing (e.g., prefer
  "configuration" to "config", etc)
• Show an example of mounting a configuration file into a container