title: two directories in git submodule
body: <p>I have few repos that requre same files in each. I discovered that I can use git submodules to do it but I got stuck.</p>
  <p>Let's say this is a file structure in each of my projects:</p>
  <p><strong>MainCatalog/</strong></p>
  <ol>
  <li>CatalogA (contains some files)</li>
  <li>CatalogB (contains some files)</li>
  <li>CatalogC (contains some files)</li>
  <li>File1</li>
  <li>File2</li>
  <li>...</li>
  </ol>
  <p>And with that structure I'd like to use a submodule for two catalogs (CatalogA and CatalogB)
  Is it possible? Or should I use two submodules for each catalog?</p>