title: Is there a way to `git submodule add` a repo *without* cloning it?
body: <p>I have a very long list of repos that I'm trying to make into one parent repo by making them all submodules. </p>
  
  <p>I've tried adding them to <code>.gitmodules</code> manually, and also to <code>.git/config</code>, but it doesn't seem to work. </p>
  
  <p>I've also tried running <code>git submodule sync</code> and <code>git submodule update --init</code>, etc, but with no luck. </p>
  
  <p>Is there a way to trick git into thinking my project has all its (~30K) submodules, without actually needing to clone them all?</p>