title: Git Adding build directory from subdirectory which is a separate git repo
body: <p>I have a react application loads into an php application (wordpress). The react application is inside a subdirectory and its a separate git repository.</p>
  <p>Now when shipping the product I want only the build directory (/js/app/build) to ship with php app.</p>
  <p>The git in master (php app) directory doesn't add the js build directory when I try to add it. What is the correct approach of this?</p>
  <p>Directory Structure:</p>
  <pre><code>php-app
  |-- js
      |-- app // git repository
          |-- build
  main.php
  file2.php
  example.php
  
  </code></pre>
  <p>NOTE: <code>/js/app/build</code> is ignored in the js app repository but it is needed to be included in php repository.</p>