title: Permanently add submodules files to main repository
body: <p>I have a plain repository $main, without submodules. Inside it I add the library $lib into /3rdparty/$lib using <code>git clone</code>. </p>
  
  <p>Also $lib repository contains several submodules which I initialize and update.</p>
  
  <p>So $main noticed that $lib's  submodules are submobules and won't push theirs files into the $main.</p>
  
  <p>Can I permanently add this submodules into $main?</p>