title: git --recursive doesn't clone submodule
body: <p>I learned that to download submodules with main repository we can use <code>--recursive</code> option when cloning main repository. </p>
  
  <p>I did the same <code>git clone --recursive git@github.com:passion/academy.git</code></p>
  
  <p>I found that it only create a empty directory of submodule but not downloaded its code. </p>
  
  <p>Do we need to do extra stuff like <code>git submodule update --init --recursive</code>  ? If yes then what is the use of <code>--recursive</code> flag when cloning main repository ?</p>