Updated extra (markdown)

extra.md

@@ -51,6 +51,29 @@ augroup PlugGx
 augroup END
 ```
 
+### Browse help files and README.md
+
+Requires [fzf](https://github.com/junegunn/fzf).
+
+```vim
+function! s:plug_help_sink(line)
+  let dir = g:plugs[a:line].dir
+  for pat in ['doc/*.txt', 'README.md']
+    let match = get(split(globpath(dir, pat), "\n"), 0, '')
+    if len(match)
+      execute 'tabedit' match
+      return
+    endif
+  endfor
+  tabnew
+  execute 'Explore' dir
+endfunction
+
+command! PlugHelp call fzf#run(fzf#wrap({
+  \ 'source': sort(keys(g:plugs)),
+  \ 'sink':   function('s:plug_help_sink')}))
+```
+
 ### Extra key bindings for PlugDiff
 
 (suggested by @sodapopcan)