title: Merge back the sub-directory created from 'git filter-repo'
body: <p>Suppose I have a repository with a folder structure like this:</p>
  <pre><code>Base
  |-dir1
  |-dir2
  | |-subdir1
  | |-subdir2
  | |-subdir3
  |-dir3
  </code></pre>
  <p>I perform 'git filter-repo' on the 'dir-2' directory. Now the folder structure I have is:</p>
  <pre><code>Base
  |-dir2
  | |-subdir1
  | |-subdir2
  | |-subdir3
  </code></pre>
  <p>After making some changes to files present in 'dir2', I want to merge it back to the original repo from where it was filtered out and have the structure back again like this:</p>
  <pre><code>Base
  |-dir1
  |-dir2 (updated with changes)
  | |-subdir1
  | |-subdir2
  | |-subdir3
  |-dir3
  </code></pre>
  <p>How do I do this while preserving history?</p>