Updated Customization (markdown)

Customization.md

@@ -75,15 +75,16 @@ let g:goyo_callbacks = [function('g:goyo_before'), function('g:goyo_after')]
 Suggested by [mm2703](https://github.com/mm2703) and [axelGschaider](https://github.com/axelGschaider) in [#16](https://github.com/junegunn/goyo.vim/issues/16)
 
 ```vim
-" Quitting whether Goyo is active or not
-ca wq :w<cr>:call Quit()<cr>
-ca q :call Quit()<cr>
-function! Quit()
-  if exists('#goyo')
-    Goyo
-  endif
-  quit
+function! g:goyo_before()
+  " ...
 endfunction
-```
 
-Or you can use `:qa` or `:wqa` instead of `:q` and `:wq`.
+function! g:goyo_after()
+  " Quit Vim if this is the only remaining buffer
+  if len(filter(range(1, bufnr('$')), 'buflisted(v:val)')) == 1
+    qa
+  endif
+endfunction
+
+let g:goyo_callbacks = [function('g:goyo_before'), function('g:goyo_after')]
+```