title: How to checkout GitHub submodule from SVN
body: <p>I am pretty new to GitHub.
    I need to check out several packages of code to build my system, most of them are on SVN. However, there is one which is on GitHub. Within this there is a submodule inside it.<br>
  My question is how to check out this submodule by using <code>svn co ...</code></p>
  
  <p>I list all components by editing </p>
  
  <pre><code>svn propedit svn:externals
  </code></pre>
  
  <p>Among them one is on GitHub. I can check out all components except that submodule.</p>
  
  <p>Thanks
  Jim </p>