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>

test/install.sh

@@ -4,6 +4,8 @@ set -e
 
 repos=(
   'junegunn/vader.vim'
+
+  # languages
   'cakebaker/scss-syntax.vim'
   'digitaltoad/vim-pug'
   'groenewege/vim-less'
@@ -11,6 +13,9 @@ repos=(
   'leafgarland/typescript-vim'
   'slm-lang/vim-slm'
   'wavded/vim-stylus'
+
+  # utility
+  'scrooloose/nerdcommenter'
 )
 
 cd "$(dirname "$0")/.."

test/test_nerdcommenter.vader

@@ -0,0 +1,40 @@
+Execute (Configure NERDCommenter to support Vue files):
+  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
+
+Given vue:
+  <template>
+    <div></div>
+  </template>
+  <style>
+    .glitters { color: gold }
+  <style>
+
+Do:
+  j\cc
+  3j\cc
+
+Expect:
+  <template>
+    <!--<div></div>-->
+  </template>
+  <style>
+    /*.glitters { color: gold }*/
+  <style>