title: Pip freeze for only project requirements
body: <p>When I run <code>pip freeze &gt; requirements.txt</code> it seems to include all installed packages. This <strong>appears</strong> to be the documented behavior.</p>
  
  <p>I have, however, done something wrong as this now includes things like Django in projects that have no business with Django.</p>
  
  <p>How do I get requirements for just this project? or in the future how do I install a package with <code>pip</code> to be used for this project. I think I missed something about a <code>virtualenv</code>.</p>