title: To monitor why git add . slow?
body: <p>Assume project where no add and commit has been done for a long time. 
  I do <code>git add .</code> but it takes too much time. 
  I  would like to estimate which files/directories are most expensive in the current case. 
  I have a good <code>.gitignore</code> file which works sufficiently but, still sometimes, I have too much and/or something too difficult to be added and committed to Git.</p>
  
  <p>I have often directories which size is from 300GB to 2 TB in my directories. 
  Although excluding them by <code>directory/*</code> and <code>directory/</code> in <code>.gitignore</code>, the addition is slow. </p>
  
  <p>How can you estimate which directories/files are too expensive to be committed? </p>