Added Dockerfile mode

custom.el

@@ -9,7 +9,7 @@
  '(elpy-eldoc-show-current-function nil)
  '(package-selected-packages
    (quote
-    (swiper mode-line-bell htmlize cython-mode blacken dired-narrow lua-mode browse-kill-ring clipmon free-keys org-link-minor-mode js2-mode js2-refactor xref-js2 python-django visual-regexp-steroids pcre2el vimrc-mode iedit transient magit dracula-theme flycheck elpy ein better-defaults ssh-config-mode yaml-mode apache-mode web-mode undo-tree))))
+    (dockerfile-mode swiper mode-line-bell htmlize cython-mode blacken dired-narrow lua-mode browse-kill-ring clipmon free-keys org-link-minor-mode js2-mode js2-refactor xref-js2 python-django visual-regexp-steroids pcre2el vimrc-mode iedit transient magit dracula-theme flycheck elpy ein better-defaults ssh-config-mode yaml-mode apache-mode web-mode undo-tree))))
 (custom-set-faces
  ;; custom-set-faces was added by Custom.
  ;; If you edit it by hand, you could mess it up, so be careful.