1. Ensure there's a syntax directory in the personal vim directory.

    mkdir -p ~/.vim/syntax
    
  2. Download the markdown syntax file and put it in this directory (e.g. markdown.vim).

  3. Affect the markdown filetype to *.mdwn files and avoid long lines (in ~/.vimrc).

    " Help autodetection
    augroup filetypedetect
        au! BufRead,BufNewFile *.mdwn setfiletype markdown
    augroup END
    
    
    " Limit the line length for this mode
    autocmd FileType markdown set tw=80
    
  4. Enjoy.