allow bootstraping packer

lua/plugins.lua

@@ -1,3 +1,16 @@
+local ensure_packer = function()
+  local fn = vim.fn
+  local install_path = fn.stdpath('data')..'/site/pack/packer/start/packer.nvim'
+  if fn.empty(fn.glob(install_path)) > 0 then
+    fn.system({'git', 'clone', '--depth', '1', 'https://github.com/wbthomason/packer.nvim', install_path})
+    vim.cmd [[packadd packer.nvim]]
+    return true
+  end
+  return false
+end
+
+local packer_bootstrap = ensure_packer()
+
 vim.cmd([[autocmd BufWritePost plugins.lua source <afile> | PackerCompile]])
 
 return require('packer').startup({function()
@@ -83,6 +96,10 @@ return require('packer').startup({function()
     config = function() require'plugins/nvim-tree' end
   }
   use 'justinmk/vim-sneak'
+
+  if packer_bootstrap then
+    require('packer').sync()
+  end
 end,
 config = {
   display = {