title: install composer-php plugin from zip file
body: <p>I'm having some issues installing a plugin into my application from a .zip file using composer.</p>
  
  <p>I have a private composer plugin in a <code>.zip</code> file. I downloaded it in my pc. I want to add this plugin into my application using composer. So that it unzip in vendor folder and work like others plugins. I am not sure is it possible or not? </p>
  
  <p>I can add it manually into autoload psr-4 classmap.  </p>