Git hook to auto-merge hotfix branches

post-receive

#!/usr/bin/env bash
  
while read oldrev newrev refname
  do
    BRANCH=$(git rev-parse --symbolic --abbrev-ref $refname)
    if [[ "$BRANCH" =~ ^hotfix/* ]]; then
      echo "   /==============================="
      echo "   | HOTFIX DETECTED ..."
      GIT_WORK_TREE=/tmp git checkout master -f -q
      GIT_WORK_TREE=/tmp git merge $BRANCH -q --comit -m "Merge $BRANCH" --no-ff
      echo "   | ... AND MERGED"
      echo "   \=============================="
      exit 0;
    else
      exit 0;
    fi
done

where should this file be placed for git to pick up and execute?