title: Cannot commit the line `Subproject commit`
body: <p>In one of my projects monitored by git, I git cloned another repo from Github. Now I noticed that in the software <code>Github for Mac</code>, there are changes about <code>Subproject commit</code>. Somehow git is referring to the cloned directory as a file with 2 lines?</p>
  
  <p><img src="https://i.stack.imgur.com/MQ2Vu.png" alt="enter image description here"></p>
  
  <p>Trying to commit the changes will throw me the error</p>
  
  <pre><code># On branch master
  # Changes not staged for commit:
  #   (use "git add &lt;file&gt;..." to update what will be committed)
  #   (use "git checkout -- &lt;file&gt;..." to discard changes in working directory)
  #   (commit or discard the untracked or modified content in submodules)
  #
  #   modified:   packages/meteor-meteor (untracked content)
  #
  no changes added to commit (use "git add" and/or "git commit -a")
   (1)
  </code></pre>
  
  <p>Doing <code>git add .</code> still gives me the same error when doing a commit. What is happening here? I do not need to track/commit/push any changes on the cloned repo, just need to pull new updates when available.</p>