title: Retrospectively add --recursive to a git repo
body: <p>If you <code>git clone</code> with <code>--recursive</code>, you can get all the git submodules too.</p>
  
  <p>If I've forgotten to add this magical flag when cloning, as can happen, how do I now go and get any submodules?</p>
  
  <p>Additionally, how can I set the recursive flag as a default for future clones?</p>