title: is it possible to add a comment to a diff file (unified)?
body: <p>I wonder if it's possible to add a certain amount of unparsed content to a diff file (unified)  that is ignored as a comment.</p>
  
  <p>One good use of this would be having git diffs augmented with important information such as from which branch is that diff from (especially when using the --full-index option, which merely displays the blob references).</p>