Add some vim markdown plugins

vim/vimrc

@@ -7,8 +7,21 @@ set tabstop=2
 set shiftwidth=2
 set expandtab
 
+set scrolloff=4
+
 set t_Co=256
 set laststatus=2
 set number
 let g:airline_powerline_fonts = 1
 let g:airline_theme='murmur'
+
+" markdown-preview
+let vim_markdown_preview_toggle=1
+let vim_markdown_preview_browser='Firefox'
+let vim_markdown_preview_use_xdg_open=1
+let vim_markdown_preview_github=1
+
+" markdown-toc
+let g:vmt_auto_update_on_save=0
+let g:vmt_dont_insert_fence=1
+let g:vmt_cycle_list_item_markers=1