title: git submodule update needed only initially?
body: <p>I'm getting a hang of git submodule (wishful thinking?) and I'm coming up with more specific questions, which is a good sign...  </p>
  
  <p>I've tried to find the which revision of the submodule the superproject refers to, in <code>.gitmodules</code> and <code>.git/config</code>, but nothing is mentioned there...<br>
  The scenario is that I'm changing submodules in their root locations (from which they're imported), and then pulling them in where they're "submoduled"...<br>
  Beyond committing from the superproject to incorporate those changes into the superproject repo, do I also need to do "<code>git update</code>" to register the new pulled in submodule commits?  </p>
  
  <p>Basically the question is:</p>
  
  <blockquote>
    <p>do I need to "<code>git submodule update</code>" only when I first clone the superproject, or after every pulling of the submodule (from its own repo)?  </p>
  </blockquote>
  
  <p>Thank you</p>