title: What does pip-compile do? What is its use?
body: <p>I am a beginner in programming and Python. I read <code>pip-compile</code>s definition in <a href="https://github.com/jazzband/pip-tools" rel="noreferrer">pip-tools documentation</a> but I could not understand. Can someone explain me this?</p>
  <p>More specifically, what does compiling <code>requirements.in</code> to produce <code>requirements.txt</code> mean?</p>