Update denite layer doc (#3896)

close #3687

autoload/SpaceVim/layers/denite.vim

@@ -6,6 +6,8 @@
 " License: GPLv3
 "=============================================================================
 
+let s:CMP = SpaceVim#api#import('vim#compatible')
+
 function! SpaceVim#layers#denite#plugins() abort
   let plugins = [
         \ ['Shougo/denite.nvim',{ 'merged' : 0, 'loadconf' : 1}],
@@ -288,6 +290,17 @@ function! s:warp_denite(cmd) abort
   doautocmd WinEnter
 endfunction
 
+function! SpaceVim#layers#denite#loadable()
+  if s:CMP.has('python3')
+    return 1
+  else
+    call SpaceVim#logger#warn('denite layer requires +python3 enabled!', 0)
+    if has('nvim')
+      call SpaceVim#logger#info('   use `pip3 install pynvim` to enabled +python3 for neovim.')
+    endif
+  endif
+endfunction
+
 " function() wrapper
 if v:version > 703 || v:version == 703 && has('patch1170')
   function! s:_function(fstr) abort

docs/cn/layers/denite.md

@@ -17,6 +17,7 @@ lang: zh
 ## 模块描述
 
 提供以 denite 为核心的异步模糊查找机制，支持模糊搜索文件、历史纪录、函数列表等。这一模块需要 Vim/Neovim 支持 `+python3`。
+
 ## 启用模块
 
 denite 模块默认并未启用，如果需要启用该模块，需要在配置文件里面加入：

docs/layers/denite.md

@@ -17,6 +17,7 @@ description: "This layers provide a heavily customized Denite centric work-flow"
 ## Description
 
 This layer is a heavily customized wrapper for denite and it's sources.
+To enable this layer, make sure your vim/neovim has `+python3` enabled.
 
 ## Install