title: How write a Symfony Flex recipe for a new bundle?
body: <p>I tried to find any documentation about using Symfony Flex but so far no luck.</p>
  
  <p>Almost all docs point to installing a bundle that uses symfony Flex, not how to create a bundle that is using it.</p>
  
  <p>I even tried to reverse engineer some of the packages but again, no luck.</p>
  
  <p>My goal is to generate a default configuration file for my bundle in <code>config/packages/my_bundle.yaml</code>. </p>
  
  <p>What I need to know is where do I need to put it and what env variables (if any) will I have available?</p>