title: Install options in requirements.in
body: <p>I use requirements.in file that I compile to generate requirements.txt</p>
  
  <pre><code>pip-compile requirements.in
  pip-sync requirements.txt
  </code></pre>
  
  <p>I can specify installation options in <code>requirements.txt</code> with </p>
  
  <pre><code>--install-options='...'
  </code></pre>
  
  <p>But if I specify the same in a <code>requirements.in</code>, I get a syntax error. How do I specify install options in a <code>requirements.in</code> file</p>