To use these files, follow these steps:

1. Either

• git clone https://github.com/zipperer/dot-emacs-for-dockerfile-and-docker-compose.git, or
• download this repository

2. $ ./use-curl-to-get-files-that-configure-emacs-for-dockerfile-and-docker-compose.sh
3. In this repository, see .emacs-example. In particular, see the section

(let ((*configure-emacs-for-docker-and-docker-compose-directory* "PATH-TO-DIRECTORY-OF-REPOSITORY-FROM-GITHUB"))
  (add-to-list 'load-path *configure-emacs-for-docker-and-docker-compose-directory*)
  (let ((configure-emacs-for-docker-and-docker-compose-file (concat *configure-emacs-for-docker-and-docker-compose-directory* "configure-emacs-for-docker-and-docker-compose.el")))
    (load configure-emacs-for-docker-and-docker-compose-file)))

Copy that section. In your ~/.emacs, paste that section. Replace PATH-TO-DIRECTORY-OF-REPOSITORY-FROM-GITHUB with the path to where made the repository. e.g. /home/your-user/example-directory/dot-emacs-for-dockerfile-and-docker-compose/. So, that line would be

(let ((*configure-emacs-for-docker-and-docker-compose-directory* "/home/your-user/example-directory/dot-emacs-for-dockerfile-and-docker-compose/"))

4. Start an instance of emacs and try M-x dockerfile-mode and M-x docker-compose-mode.
5. Observe emacs choose the mode when C-x C-f Dockerfile and C-x C-f docker-compose.yml