markdown-mode (gfm-mode)

init.el

(require 'markdown-mode)

(setq my-markdown-gfm-command "/usr/local/bin/marked")
(setq my-markdown-command "/usr/local/bin/markdown")

(cond
 ((file-exists-p my-markdown-gfm-command)
  (setq markdown-command my-markdown-gfm-command)
  (setq markdown-command-needs-filename t))
 ((file-exists-p my-markdown-command)
  (setq markdown-command my-markdown-command)))

(add-to-list 'auto-mode-alist '("\\.md\\'" . gfm-mode))

(add-hook 'visual-line-mode-hook
	  '(lambda()
	     (setq word-wrap nil)))

(add-hook 'gfm-mode-hook
 	  '(lambda()
	     (setq indent-tabs-mode nil)
	     (setq tab-width 4)))