title: Git post-receive - how to check if pushed branch is merged with master
body: <p>In our team we are usually pushing all tasks into separate branches, and after that release-manager review those branches and merge them into 'master' branch</p>
  
  <p>Sometimes team-members forget to merge their branches with master branch(before pushing) - so what I'm trying to do is - output a message "Please merge with master" after user push - I assume I need to check something on post-receive hook on remote.. is there some examples?.. or what I should basically do ?</p>
  
  <p>update: main reason for this - minimize number of potential conflicts (since committer(not release-manager) will resolve them)</p>