Note on single quotes (#33)

README.md

@@ -37,6 +37,7 @@ Edit your .vimrc
 ```vim
 call plug#begin('~/.vim/plugged')
 
+" Make sure you use single quotes
 Plug 'junegunn/seoul256.vim'
 Plug 'junegunn/vim-easy-align'
 Plug 'scrooloose/nerdtree', { 'on':  'NERDTreeToggle' }