title: allow subdirectory index but no other pages in subdirectory
body: <p>In robots.txt...</p>
  
  <p>I want to allow the index or homepage of the directory.</p>
  
  <pre><code>/landing/
  </code></pre>
  
  <p>I don't want to allow any other pages within the directory.</p>
  
  <pre><code>/landing/page  
  /landing/anypage
  </code></pre>
  
  <p>How can this be done?</p>