Docs: provide lua examples for heretics like myself. about vim-quickui

[wookayin]

This plugin uses an old-fashioned vimscript config style, so you have to do something like:

{
  'skywind3000/vim-quickui',
  init = function ()
     -- Add some config to run BEFORE plugin/quickui.vim loads
     vim.g.quickui_border_style = 2
  end,
  config = function ()
     -- Add some config AFTER plugin/quickui.vim has been loaded
     vim.cmd [[ hi! QuickPreview guibg=#262d2d ]]
  end,
}

[airtonix]

Would you be open to a PR that enhances the README?