Add note to FAQ about nerdcommenter, and add tests for it

readme.md

@@ -92,3 +92,35 @@ autocmd BufRead,BufNewFile *.vue setlocal filetype=vue.html.javascript.css
 
 :warning: This may cause problems, because some plugins will then treat the
 whole buffer as html/javascript/css instead of only the part inside the tags.
+
+### How can I use NERDCommenter in Vue files?
+
+<details>
+<summary>
+To use NERDCommenter with Vue files, you can use its "hooks" feature to
+temporarily change the filetype. Click for an example.
+</summary>
+
+```vim
+let g:ft = ''
+function! NERDCommenter_before()
+  if &ft == 'vue'
+    let g:ft = 'vue'
+    let stack = synstack(line('.'), col('.'))
+    if len(stack) > 0
+      let syn = synIDattr((stack)[0], 'name')
+      if len(syn) > 0
+        exe 'setf ' . substitute(tolower(syn), '^vue_', '', '')
+      endif
+    endif
+  endif
+endfunction
+function! NERDCommenter_after()
+  if g:ft == 'vue'
+    setf vue
+    let g:ft = ''
+  endif
+endfunction
+```
+
+</details>