https://www.markdownguide.org/basic-syntax/
tl;dr
Para Instalar o modo markdown no emacs, inserir o código abaixo no init.el
(use-package markdown-mode
:ensure t
:commands (markdown-mode gfm-mode)
:mode (("README\\.md\\'" . gfm-mode)
("\\.md\\'" . markdown-mode)
("\\.markdown\\'" . markdown-mode)))