title: Deny direct pushes to main repository on github
body: <p>We use pull-requests workflow for our projects. Each developer has own fork of a project.
  For example I have two repositories: upstream(main repo) and origin(fork of main repo). When I want to commit something I make a push to origin(my fork) and create a pull request from it to main repo.</p>
  
  <p>Everything works great and it's a really good way to do code reviews but this is just a convention. Sometimes remote contractors do direct pushes to main repo(maybe it's just an accident:)).</p>
  
  <p>Is there any explicit way to deny direct pushes to main repo?</p>
  
  <p>Hooks don't help in this case because each developer can disable them</p>